Update Longest Palindrome Substring.cpp

Author: Anshul123kumar

Dynamic Programming/Longest Palindrome substring/Longest Palindrome Substring.cpp

@@ -1 +1,49 @@
+class Solution {
+public:
+    string longestPalindrome(string s) {
+        int n = s.length();
+        bool dp[n][n];
+        
+        int ans = 1;
+        int st = 0;
+        
+        ///fill all substring of length 1
+        for(int i=0; i<n; i++){
+            dp[i][i] = true;
+        }
+        
+        ///fill all substring of length 2
+        for(int i=0; i<n-1; i++){
+            if(s[i] == s[i+1]){
+                ans = 2;
+                dp[i][i+1] = true;
+                st = i;
+            }
+            else{
+                dp[i][i+1] = false;
+            }
+        }
+        
+        //dp[i][j] means start at i and end at j...
+         ///fill the rest of the table
+        for(int l=3; l<=n; l++){  //for substring of length 3 and more...
+            for(int i=0; i<=n-l; i++){       //n-l is the max index where index of                                                        //particular substring of length l end
+                int end = i+l-1;
+                
+                if(s[i] == s[end]){
+                    dp[i][end] = dp[i+1][end-1];
+                    if(dp[i][end] == true){
+                        ans = l;
+                        st = i;
+                    }
+                }
+                else{
+                    dp[i][end] = false;
+                }
+            }
+        }
+        //printing the substring
+        return s.substr(st, ans);
+    }
+};