day 13

Author: sachuverma

Leetcode Daily Challenge/June-2021/13. Palindrome Pairs.cpp

@@ -0,0 +1,97 @@
+/*
+Palindrome Pairs
+================
+
+Given a list of unique words, return all the pairs of the distinct indices (i, j) in the given list, so that the concatenation of the two words words[i] + words[j] is a palindrome.
+
+Example 1:
+Input: words = ["abcd","dcba","lls","s","sssll"]
+Output: [[0,1],[1,0],[3,2],[2,4]]
+Explanation: The palindromes are ["dcbaabcd","abcddcba","slls","llssssll"]
+
+Example 2:
+Input: words = ["bat","tab","cat"]
+Output: [[0,1],[1,0]]
+Explanation: The palindromes are ["battab","tabbat"]
+
+Example 3:
+Input: words = ["a",""]
+Output: [[0,1],[1,0]]
+
+Constraints:
+1 <= words.length <= 5000
+0 <= words[i].length <= 300
+words[i] consists of lower-case English letters.
+*/
+
+class Solution
+{
+public:
+  bool palendrome(string str)
+  {
+    int i = 0, j = str.size() - 1;
+    while (i < j)
+    {
+      if (str[i++] != str[j--])
+        return false;
+    }
+    return true;
+  }
+
+  vector<vector<int>> palindromePairs(vector<string> &arr)
+  {
+    unordered_map<string, int> words;
+    vector<vector<int>> ans;
+    vector<bool> isPal(arr.size(), 0);
+
+    for (int i = 0; i < arr.size(); ++i)
+      isPal[i] = palendrome(arr[i]);
+
+    for (int i = 0; i < arr.size(); ++i)
+      words[arr[i]] = i;
+
+    for (int i = 0; i < arr.size(); ++i)
+    {
+      // first type, right me add krke palendrome bnao
+      // ie, we have to find prefix ka reverse
+      string curr = "";
+      for (int j = 0; j < arr[i].size(); ++j)
+      {
+        curr = arr[i][j] + curr;
+        if (words.count(curr) && words[curr] != i && palendrome(arr[i] + curr))
+        {
+          ans.push_back({i, words[curr]});
+        }
+      }
+
+      // phir suffix ka reverse dekhna hai
+      curr = "";
+      for (int j = arr[i].size() - 1; j > 0; --j)
+      {
+        curr += arr[i][j];
+        if (words.count(curr) && words[curr] != i && palendrome(curr + arr[i]))
+        {
+          ans.push_back({words[curr], i});
+        }
+      }
+    }
+
+    // match empty string with all palendromes
+    for (int i = 0; i < arr.size(); ++i)
+    {
+      if (arr[i] == "")
+      {
+        for (int j = 0; j < arr.size(); ++j)
+        {
+          if (i != j && isPal[j])
+          {
+            ans.push_back({i, j});
+            ans.push_back({j, i});
+          }
+        }
+      }
+    }
+
+    return ans;
+  }
+};

Leetcode Daily Challenge/June-2021/README.md

@@ -13,4 +13,5 @@
 | 9.  | [Jump Game VI](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/604/week-2-june-8th-june-14th/3773/) [cpp](./09.%20Jump%20Game%20VI.cpp)                                                                                                     |
 | 10. | [My Calendar I](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/604/week-2-june-8th-june-14th/3774/) [cpp](./10.%20My%20Calendar%20I.cpp)                                                                                                   |
 | 11. | [Stone Game VII](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/604/week-2-june-8th-june-14th/3775/) [cpp](./11.%20Stone%20Game%20VII.cpp)                                                                                                 |
-| 12. | [Minimum Number of Refueling Stops](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/604/week-2-june-8th-june-14th/3776/) [cpp](./12.%20Minimum%20Number%20of%20Refueling%20Stops.cpp)                                                                                                 |
+| 12. | [Minimum Number of Refueling Stops](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/604/week-2-june-8th-june-14th/3776/) [cpp](./12.%20Minimum%20Number%20of%20Refueling%20Stops.cpp)                                                       |
+| 13. | [Palindrome Pairs](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/604/week-2-june-8th-june-14th/3777/) [cpp](./13.%20Palindrome%20Pairs.cpp)                                                                                               |