day 26

Author: sachuverma

Leetcode Daily Challenge/June-2021/26. Count of Smaller Numbers After Self.cpp

@@ -0,0 +1,101 @@
+/*
+Count of Smaller Numbers After Self
+===================================
+
+You are given an integer array nums and you have to return a new counts array. The counts array has the property where counts[i] is the number of smaller elements to the right of nums[i].
+
+Example 1:
+Input: nums = [5,2,6,1]
+Output: [2,1,1,0]
+Explanation:
+To the right of 5 there are 2 smaller elements (2 and 1).
+To the right of 2 there is only 1 smaller element (1).
+To the right of 6 there is 1 smaller element (1).
+To the right of 1 there is 0 smaller element.
+
+Example 2:
+Input: nums = [-1]
+Output: [0]
+
+Example 3:
+Input: nums = [-1,-1]
+Output: [0,0]
+
+Constraints:
+1 <= nums.length <= 105
+-104 <= nums[i] <= 104
+*/
+
+class Solution
+{
+public:
+  vector<pair<int, int>> temp, B;
+
+  void crossInversion(int st, int en, vector<int> &A)
+  {
+    int mid = (st + en) / 2;
+    int i = st, j = mid + 1;
+    int k = st;
+
+    while (i <= mid && j <= en)
+    {
+      if (B[i].first <= B[j].first)
+      {
+        temp[k] = B[j];
+        j++;
+        k++;
+      }
+      else
+      {
+        temp[k] = B[i];
+        A[B[i].second] += (en - j + 1);
+        i++;
+        k++;
+      }
+    }
+
+    while (i <= mid)
+    {
+      temp[k] = B[i];
+      A[B[i].second] += (en - j + 1);
+      i++;
+      k++;
+    }
+
+    while (j <= en)
+    {
+      temp[k] = B[j];
+      j++;
+      k++;
+    }
+
+    for (int i = st; i <= en; ++i)
+      B[i] = temp[i];
+  }
+
+  void countInversion(int st, int en, vector<int> &A)
+  {
+    if (st >= en)
+      return;
+    int mid = (st + en) / 2;
+
+    countInversion(st, mid, A);
+    countInversion(mid + 1, en, A);
+    crossInversion(st, en, A);
+  }
+
+  vector<int> countSmaller(vector<int> &A)
+  {
+    int n = A.size();
+
+    temp = vector<pair<int, int>>(n, {0, 0});
+    B = vector<pair<int, int>>(n, {0, 0});
+    vector<int> ans(n, 0);
+
+    for (int i = 0; i < n; ++i)
+      B[i] = {A[i], i};
+
+    countInversion(0, n - 1, ans);
+    return ans;
+  }
+};

Leetcode Daily Challenge/June-2021/README.md

@@ -27,3 +27,4 @@
 | 23. | [Reverse Linked List II](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/606/week-4-june-22nd-june-28th/3789/) [cpp](./23.%20Reverse%20Linked%20List%20II.cpp)                                                                              |
 | 24. | [Out of Boundary Paths](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/606/week-4-june-22nd-june-28th/3790/) [cpp](./24.%20Out%20of%20Boundary%20Paths.cpp)                                                                                |
 | 25. | [Redundant Connection](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/606/week-4-june-22nd-june-28th/3791/) [cpp](./25.%20Redundant%20Connection.cpp)                                                                                |
+| 26. | [Count of Smaller Numbers After Self](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/606/week-4-june-22nd-june-28th/3792/) [cpp](./26.%20Count%20of%20Smaller%20Numbers%20After%20Self.cpp)                                                                                |