New Problem Solution -"Maximize Palindrome Length From Subsequences"

Author: haoel

README.md

@@ -32,6 +32,7 @@ LeetCode
 |1775|[Equal Sum Arrays With Minimum Number of Operations](https://leetcode.com/problems/equal-sum-arrays-with-minimum-number-of-operations/) | [C++](./algorithms/cpp/equalSumArraysWithMinimumNumberOfOperations/EqualSumArraysWithMinimumNumberOfOperations.cpp)|Medium|
 |1774|[Closest Dessert Cost](https://leetcode.com/problems/closest-dessert-cost/) | [C++](./algorithms/cpp/closestDessertCost/ClosestDessertCost.cpp)|Medium|
 |1773|[Count Items Matching a Rule](https://leetcode.com/problems/count-items-matching-a-rule/) | [C++](./algorithms/cpp/countItemsMatchingARule/CountItemsMatchingARule.cpp)|Easy|
+|1771|[Maximize Palindrome Length From Subsequences](https://leetcode.com/problems/maximize-palindrome-length-from-subsequences/) | [C++](./algorithms/cpp/maximizePalindromeLengthFromSubsequences/MaximizePalindromeLengthFromSubsequences.cpp)|Hard|
 |1769|[Minimum Number of Operations to Move All Balls to Each Box](https://leetcode.com/problems/minimum-number-of-operations-to-move-all-balls-to-each-box/) | [C++](./algorithms/cpp/minimumNumberOfOperationsToMoveAllBallsToEachBox/MinimumNumberOfOperationsToMoveAllBallsToEachBox.cpp)|Medium|
 |1768|[Merge Strings Alternately](https://leetcode.com/problems/merge-strings-alternately/) | [C++](./algorithms/cpp/mergeStringsAlternately/MergeStringsAlternately.cpp)|Easy|
 |1765|[Map of Highest Peak](https://leetcode.com/problems/map-of-highest-peak/) | [C++](./algorithms/cpp/mapOfHighestPeak/MapOfHighestPeak.cpp)|Medium|

algorithms/cpp/maximizePalindromeLengthFromSubsequences/MaximizePalindromeLengthFromSubsequences.cpp

@@ -0,0 +1,104 @@
+// Source : https://leetcode.com/problems/maximize-palindrome-length-from-subsequences/
+// Author : Hao Chen
+// Date   : 2021-03-27
+
+/***************************************************************************************************** 
+ *
+ * You are given two strings, word1 and word2. You want to construct a string in the following manner:
+ * 
+ * 	Choose some non-empty subsequence subsequence1 from word1.
+ * 	Choose some non-empty subsequence subsequence2 from word2.
+ * 	Concatenate the subsequences: subsequence1 + subsequence2, to make the string.
+ * 
+ * Return the length of the longest palindrome that can be constructed in the described manner. If no 
+ * palindromes can be constructed, return 0.
+ * 
+ * A subsequence of a string s is a string that can be made by deleting some (possibly none) 
+ * characters from s without changing the order of the remaining characters.
+ * 
+ * A palindrome is a string that reads the same forward as well as backward.
+ * 
+ * Example 1:
+ * 
+ * Input: word1 = "cacb", word2 = "cbba"
+ * Output: 5
+ * Explanation: Choose "ab" from word1 and "cba" from word2 to make "abcba", which is a palindrome.
+ * 
+ * Example 2:
+ * 
+ * Input: word1 = "ab", word2 = "ab"
+ * Output: 3
+ * Explanation: Choose "ab" from word1 and "a" from word2 to make "aba", which is a palindrome.
+ * 
+ * Example 3:
+ * 
+ * Input: word1 = "aa", word2 = "bb"
+ * Output: 0
+ * Explanation: You cannot construct a palindrome from the described method, so return 0.
+ * 
+ * Constraints:
+ * 
+ * 	1 <= word1.length, word2.length <= 1000
+ * 	word1 and word2 consist of lowercase English letters.
+ ******************************************************************************************************/
+
+/*
+    // The basic algorthim come from
+    // https://leetcode.com/problems/longest-palindromic-subsequence/
+    
+    int longestPalindromeSubseq(string& s) {
+        int n = s.size(); 
+        vector<vector<int>> dp(n, vector<int>(n, 0));
+
+        for (int start = n-1; start>=0; start--) {
+            for (int end = start ; end < n ; end++) {
+                if (start == end) {
+                    dp[start][end] = 1;
+                    continue;
+                }
+                if (s[start] == s[end]) {
+                    dp[start][end] = dp[start+1][end-1] + 2;
+                }else{
+                     dp[start][end] = max (dp[start+1][end], dp[start][end-1]);
+                }
+
+            }
+        }
+        return dp[0][n-1];
+    }
+*/
+
+
+class Solution {
+
+public:
+    int longestPalindrome(string word1, string word2) {
+        
+        string s = word1 + word2;
+        int n = s.size(); 
+        vector<vector<int>> dp(n, vector<int>(n, 0));
+        
+        int result = 0; 
+        for (int start = n-1; start>=0; start--) {
+            for (int end = start ; end < n ; end++) {
+                if (start == end) {
+                    dp[start][end] = 1;
+                    continue;
+                }
+                if (s[start] == s[end]) {
+                    dp[start][end] = dp[start+1][end-1] + 2;
+                    // <-----------  different -----------> 
+                    //only consider when `start` and `end` in different string.
+                    if (start < word1.size() && end >= word1.size()){
+                        result = max(result, dp[start][end]);
+                    }
+                    // <-----------  different -----------> 
+                }else{
+                     dp[start][end] = max (dp[start+1][end], dp[start][end-1]);
+                }
+                
+            }
+        }  
+        return result;
+    }
+};