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add leetcode solutions ⚡
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‎leetcode/0384-shuffle-an-array/0384-shuffle-an-array.cpp

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class Solution {
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vector<int> original;
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int n;
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public:
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Solution(vector<int>& nums) {
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original = nums;
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n = original.size();
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}
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vector<int> reset() {
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return original;
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}
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vector<int> shuffle() {
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vector<int> shuffled = original;
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for (int i = n - 1, leftSize = n; i >= 0; i--, leftSize--) {
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int j = rand() % leftSize;
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swap(shuffled[i], shuffled[j]);
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}
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return shuffled;
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}
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};

‎leetcode/0384-shuffle-an-array/NOTES.md

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​

‎leetcode/0384-shuffle-an-array/README.md

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<h2><a href="https://leetcode.com/problems/shuffle-an-array/">384. Shuffle an Array</a></h2><h3>Medium</h3><hr><div><p>Given an integer array <code>nums</code>, design an algorithm to randomly shuffle the array. All permutations of the array should be <strong>equally likely</strong> as a result of the shuffling.</p>
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<p>Implement the <code>Solution</code> class:</p>
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<ul>
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<li><code>Solution(int[] nums)</code> Initializes the object with the integer array <code>nums</code>.</li>
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<li><code>int[] reset()</code> Resets the array to its original configuration and returns it.</li>
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<li><code>int[] shuffle()</code> Returns a random shuffling of the array.</li>
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</ul>
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<p>&nbsp;</p>
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<p><strong class="example">Example 1:</strong></p>
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<pre><strong>Input</strong>
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["Solution", "shuffle", "reset", "shuffle"]
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[[[1, 2, 3]], [], [], []]
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<strong>Output</strong>
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[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]
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<strong>Explanation</strong>
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Solution solution = new Solution([1, 2, 3]);
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solution.shuffle(); // Shuffle the array [1,2,3] and return its result.
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// Any permutation of [1,2,3] must be equally likely to be returned.
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// Example: return [3, 1, 2]
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solution.reset(); // Resets the array back to its original configuration [1,2,3]. Return [1, 2, 3]
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solution.shuffle(); // Returns the random shuffling of array [1,2,3]. Example: return [1, 3, 2]
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</pre>
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<p>&nbsp;</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 &lt;= nums.length &lt;= 50</code></li>
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<li><code>-10<sup>6</sup> &lt;= nums[i] &lt;= 10<sup>6</sup></code></li>
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<li>All the elements of <code>nums</code> are <strong>unique</strong>.</li>
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<li>At most <code>10<sup>4</sup></code> calls <strong>in total</strong> will be made to <code>reset</code> and <code>shuffle</code>.</li>
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</ul>
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</div>

‎leetcode/0403-frog-jump/0403-frog-jump.cpp

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class Solution {
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public:
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bool canCross(vector<int>& s) {
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if (s[0] + 1 != s[1]) return false;
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int n = s.size() - 1;
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unordered_map<string, bool> bag;
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auto gen_key = [](auto l, auto ...r) {
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return (to_string(l) + ... + ("-" + to_string(r)));
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};
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function<bool(int, int, int)> go = [&](auto i, auto val, auto offset) {
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if (val < s[i]) return false;
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if ( i == n ) return val == s[i];
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auto key = gen_key(i, val, offset);
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if (bag.count(key)) return bag[key];
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if (val > s[i]) return bag[key] = go(i + 1, val, offset);
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auto paths = go(i + 1, val + offset, offset)
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|| go(i + 1, val + offset + 1, offset + 1)
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|| go(i + 1, val + offset - 1, offset - 1);
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return bag[key] = paths;
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};
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return go(1, 1, 1);
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}
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};

‎leetcode/0403-frog-jump/NOTES.md

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​

‎leetcode/0403-frog-jump/README.md

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<h2><a href="https://leetcode.com/problems/frog-jump/">403. Frog Jump</a></h2><h3>Hard</h3><hr><div><p>A frog is crossing a river. The river is divided into some number of units, and at each unit, there may or may not exist a stone. The frog can jump on a stone, but it must not jump into the water.</p>
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<p>Given a list of <code>stones</code>' positions (in units) in sorted <strong>ascending order</strong>, determine if the frog can cross the river by landing on the last stone. Initially, the frog is on the first stone and assumes the first jump must be <code>1</code> unit.</p>
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<p>If the frog's last jump was <code>k</code> units, its next jump must be either <code>k - 1</code>, <code>k</code>, or <code>k + 1</code> units. The frog can only jump in the forward direction.</p>
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<p>&nbsp;</p>
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<p><strong class="example">Example 1:</strong></p>
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<pre><strong>Input:</strong> stones = [0,1,3,5,6,8,12,17]
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<strong>Output:</strong> true
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<strong>Explanation:</strong> The frog can jump to the last stone by jumping 1 unit to the 2nd stone, then 2 units to the 3rd stone, then 2 units to the 4th stone, then 3 units to the 6th stone, 4 units to the 7th stone, and 5 units to the 8th stone.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre><strong>Input:</strong> stones = [0,1,2,3,4,8,9,11]
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<strong>Output:</strong> false
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<strong>Explanation:</strong> There is no way to jump to the last stone as the gap between the 5th and 6th stone is too large.
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</pre>
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<p>&nbsp;</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>2 &lt;= stones.length &lt;= 2000</code></li>
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<li><code>0 &lt;= stones[i] &lt;= 2<sup>31</sup> - 1</code></li>
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<li><code>stones[0] == 0</code></li>
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<li><code>stones</code>&nbsp;is sorted in a strictly increasing order.</li>
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</ul>
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</div>

‎leetcode/0423-reconstruct-original-digits-from-english/0423-reconstruct-original-digits-from-english.cpp

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class Solution {
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public:
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string originalDigits(string s) {
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vector<string> words = {"zero", "two", "four", "six", "eight",
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"one", "three", "five", "seven", "nine"};
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vector<int> nums = {0, 2, 4, 6, 8, 1, 3, 5, 7, 9};
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vector<int> distinct_char = {'z', 'w', 'u', 'x', 'g', 'o', 'r', 'f', 'v', 'i'};
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vector<int> counts(26, 0);
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string result;
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for (auto ch : s) counts[ch-'a']++;
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for (int i = 0; i < 10; i++) {
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int count = counts[distinct_char[i]-'a'];
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for (int j = 0; j < words[i].size(); j++)
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counts[words[i][j]-'a'] -= count;
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while (count--)
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result += to_string(nums[i]);
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}
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sort(result.begin(), result.end());
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return result;
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}
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};

‎leetcode/0423-reconstruct-original-digits-from-english/NOTES.md

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​

‎leetcode/0423-reconstruct-original-digits-from-english/README.md

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<h2><a href="https://leetcode.com/problems/reconstruct-original-digits-from-english/">423. Reconstruct Original Digits from English</a></h2><h3>Medium</h3><hr><div><p>Given a string <code>s</code> containing an out-of-order English representation of digits <code>0-9</code>, return <em>the digits in <strong>ascending</strong> order</em>.</p>
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<p>&nbsp;</p>
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<p><strong class="example">Example 1:</strong></p>
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<pre><strong>Input:</strong> s = "owoztneoer"
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<strong>Output:</strong> "012"
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</pre><p><strong class="example">Example 2:</strong></p>
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<pre><strong>Input:</strong> s = "fviefuro"
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<strong>Output:</strong> "45"
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</pre>
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<p>&nbsp;</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
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<li><code>s[i]</code> is one of the characters <code>["e","g","f","i","h","o","n","s","r","u","t","w","v","x","z"]</code>.</li>
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<li><code>s</code> is <strong>guaranteed</strong> to be valid.</li>
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</ul>
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</div>

‎leetcode/0454-4sum-ii/0454-4sum-ii.cpp

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// Gets TLE
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/*
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class Solution {
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public:
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int fourSumCount(vector<int>& one,
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vector<int>& two,
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vector<int>& three,
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vector<int>& four, int res = 0) {
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for (auto a: one)
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for (auto b: two)
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for (auto c: three)
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for (auto d: four)
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res += (a + b + c + d == 0);
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return res;
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}
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};
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*/
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class Solution {
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public:
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int fourSumCount(vector<int>& one,
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vector<int>& two,
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vector<int>& three,
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vector<int>& four, int res = 0) {
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unordered_map<int,int> mp;
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for (auto a: one)
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for (auto b: two)
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mp[a + b]++;
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for (auto c: three)
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for (auto d: four)
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if (mp.count(0 - c - d)) res += mp[0 - c - d];
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return res;
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}
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};

‎leetcode/0454-4sum-ii/NOTES.md

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​

‎leetcode/0454-4sum-ii/README.md

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<h2><a href="https://leetcode.com/problems/4sum-ii/">454. 4Sum II</a></h2><h3>Medium</h3><hr><div><p>Given four integer arrays <code>nums1</code>, <code>nums2</code>, <code>nums3</code>, and <code>nums4</code> all of length <code>n</code>, return the number of tuples <code>(i, j, k, l)</code> such that:</p>
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<ul>
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<li><code>0 &lt;= i, j, k, l &lt; n</code></li>
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<li><code>nums1[i] + nums2[j] + nums3[k] + nums4[l] == 0</code></li>
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</ul>
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<p>&nbsp;</p>
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<p><strong class="example">Example 1:</strong></p>
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<pre><strong>Input:</strong> nums1 = [1,2], nums2 = [-2,-1], nums3 = [-1,2], nums4 = [0,2]
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<strong>Output:</strong> 2
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<strong>Explanation:</strong>
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The two tuples are:
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1. (0, 0, 0, 1) -&gt; nums1[0] + nums2[0] + nums3[0] + nums4[1] = 1 + (-2) + (-1) + 2 = 0
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2. (1, 1, 0, 0) -&gt; nums1[1] + nums2[1] + nums3[0] + nums4[0] = 2 + (-1) + (-1) + 0 = 0
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre><strong>Input:</strong> nums1 = [0], nums2 = [0], nums3 = [0], nums4 = [0]
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<strong>Output:</strong> 1
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</pre>
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<p>&nbsp;</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>n == nums1.length</code></li>
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<li><code>n == nums2.length</code></li>
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<li><code>n == nums3.length</code></li>
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<li><code>n == nums4.length</code></li>
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<li><code>1 &lt;= n &lt;= 200</code></li>
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<li><code>-2<sup>28</sup> &lt;= nums1[i], nums2[i], nums3[i], nums4[i] &lt;= 2<sup>28</sup></code></li>
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</ul>
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</div>

‎leetcode/0486-predict-the-winner/0486-predict-the-winner.cpp

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class Solution {
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public:
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bool PredictTheWinner(vector<int>& nums) {
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auto gen_key = [](auto l, auto ...r) {
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return (to_string(l) + ... + ("-" + to_string(r)));
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};
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unordered_map<string, int> c;
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auto sum = accumulate(nums.begin(), nums.end(), 0);
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function<int(int, int, bool)> go = [&](auto l, auto r, auto is_a) {
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if (l > r) return 0;
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auto key = gen_key(l, r, is_a);
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if (c.count(key)) return c[key];
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auto l_taken = (is_a ? nums[l]: 0) + go(l + 1, r, !is_a),
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r_taken = (is_a ? nums[r]: 0) + go(l, r - 1, !is_a);
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return c[key] = is_a ? max(l_taken, r_taken): min(l_taken, r_taken);
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};
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auto a_score = go(0, nums.size() - 1, true);
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return 2 * a_score >= sum;
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}
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};

‎leetcode/0486-predict-the-winner/NOTES.md

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​

‎leetcode/0486-predict-the-winner/README.md

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<h2><a href="https://leetcode.com/problems/predict-the-winner/">486. Predict the Winner</a></h2><h3>Medium</h3><hr><div><p>You are given an integer array <code>nums</code>. Two players are playing a game with this array: player 1 and player 2.</p>
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<p>Player 1 and player 2 take turns, with player 1 starting first. Both players start the game with a score of <code>0</code>. At each turn, the player takes one of the numbers from either end of the array (i.e., <code>nums[0]</code> or <code>nums[nums.length - 1]</code>) which reduces the size of the array by <code>1</code>. The player adds the chosen number to their score. The game ends when there are no more elements in the array.</p>
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<p>Return <code>true</code> if Player 1 can win the game. If the scores of both players are equal, then player 1 is still the winner, and you should also return <code>true</code>. You may assume that both players are playing optimally.</p>
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<p>&nbsp;</p>
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<p><strong class="example">Example 1:</strong></p>
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<pre><strong>Input:</strong> nums = [1,5,2]
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<strong>Output:</strong> false
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<strong>Explanation:</strong> Initially, player 1 can choose between 1 and 2.
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If he chooses 2 (or 1), then player 2 can choose from 1 (or 2) and 5. If player 2 chooses 5, then player 1 will be left with 1 (or 2).
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So, final score of player 1 is 1 + 2 = 3, and player 2 is 5.
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Hence, player 1 will never be the winner and you need to return false.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre><strong>Input:</strong> nums = [1,5,233,7]
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<strong>Output:</strong> true
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<strong>Explanation:</strong> Player 1 first chooses 1. Then player 2 has to choose between 5 and 7. No matter which number player 2 choose, player 1 can choose 233.
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Finally, player 1 has more score (234) than player 2 (12), so you need to return True representing player1 can win.
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</pre>
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<p>&nbsp;</p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 &lt;= nums.length &lt;= 20</code></li>
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<li><code>0 &lt;= nums[i] &lt;= 10<sup>7</sup></code></li>
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</ul>
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</div>

‎leetcode/0577-employee-bonus/0577-employee-bonus.sql

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# Write your MySQL query statement below
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select Employee.name, Bonus.bonus from Employee
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left join Bonus on Employee.empId = Bonus.empId
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where Bonus.bonus < 1000 or Bonus.bonus is NULL;

‎leetcode/0577-employee-bonus/NOTES.md

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​

‎leetcode/0577-employee-bonus/README.md

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<h2><a href="https://leetcode.com/problems/employee-bonus/">577. Employee Bonus</a></h2><h3>Easy</h3><hr><div class="sql-schema-wrapper__3VBi"><a class="sql-schema-link__3cEg">SQL Schema<svg viewBox="0 0 24 24" width="1em" height="1em" class="icon__1Md2"><path fill-rule="evenodd" d="M10 6L8.59 7.41 13.17 12l-4.58 4.59L10 18l6-6z"></path></svg></a></div><div><p>Table: <code>Employee</code></p>
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<pre>+-------------+---------+
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| Column Name | Type |
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+-------------+---------+
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| empId | int |
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| name | varchar |
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| supervisor | int |
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| salary | int |
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+-------------+---------+
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empId is the primary key column for this table.
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Each row of this table indicates the name and the ID of an employee in addition to their salary and the id of their manager.
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</pre>
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<p>&nbsp;</p>
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<p>Table: <code>Bonus</code></p>
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<pre>+-------------+------+
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| Column Name | Type |
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+-------------+------+
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| empId | int |
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| bonus | int |
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+-------------+------+
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empId is the primary key column for this table.
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empId is a foreign key to empId from the Employee table.
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Each row of this table contains the id of an employee and their respective bonus.
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</pre>
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<p>&nbsp;</p>
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<p>Write an SQL query to report the name and bonus amount of each employee with a bonus <strong>less than</strong> <code>1000</code>.</p>
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<p>Return the result table in <strong>any order</strong>.</p>
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<p>The query result format is in the following example.</p>
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<p>&nbsp;</p>
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<p><strong class="example">Example 1:</strong></p>
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<pre><strong>Input:</strong>
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Employee table:
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+-------+--------+------------+--------+
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| empId | name | supervisor | salary |
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+-------+--------+------------+--------+
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| 3 | Brad | null | 4000 |
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| 1 | John | 3 | 1000 |
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| 2 | Dan | 3 | 2000 |
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| 4 | Thomas | 3 | 4000 |
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+-------+--------+------------+--------+
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Bonus table:
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+-------+-------+
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| empId | bonus |
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+-------+-------+
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| 2 | 500 |
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| 4 | 2000 |
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+-------+-------+
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<strong>Output:</strong>
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+------+-------+
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| name | bonus |
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+------+-------+
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| Brad | null |
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| John | null |
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| Dan | 500 |
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+------+-------+
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</pre>
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</div>

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