Added Longest Palindromic Subsequence code

Added Longest Palindromic Subsequence code in C++.

LongestPalindromicSubsequence.cpp

@@ -0,0 +1,25 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+int LPS(string s1){
+    string s2 = s1;
+    reverse(s2.begin(), s2.end());
+    vector<vector<int>> dp(s1.length()+1, vector<int>(s2.length()+1, 0));
+    for(int i = 1; i<=s1.length(); i++){
+        for(int j = 1; j<= s2.length(); j++){
+            if(s1[i-1] == s2[j-1])
+                dp[i][j] = 1+ dp[i-1][j-1];
+            else
+                dp[i][j] = max(dp[i-1][j], dp[i][j-1]);
+        }
+    }
+    return dp[s1.length()][s2.length()];
+}
+int main()
+{
+    string s1;
+    cin>>s1;
+    int res = LPS(s1);
+    cout<< res<<endl;
+    return 0;
+}