Added solution - LeetHub

Count Palindromic Subsequences - GFG/count-palindromic-subsequences.cpp

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+//{ Driver Code Starts
+// Counts Palindromic Subsequence in a given String
+#include<bits/stdc++.h>
+using namespace std;
+
+// } Driver Code Ends
+class Solution{
+    public:
+    /*You are required to complete below method */
+    long long int  countPS(string str)
+    {
+       //Your code here
+           long long mod = 1e9+7;
+        int n = str.size();
+        vector<vector<int>> dp(n,vector<int>(n,0));
+        int cnt = 0;
+        for(int g = 0 ; g<n; g++){
+            for(int i = 0 ,j=g;j<n;j++,i++){
+                if(g==0){
+                    dp[i][j]=1;
+                }
+                else if(g==1){
+                    if(str[i]==str[j]){
+                        dp[i][j] = 3;
+                    }
+                    else{
+                        dp[i][j] = 2;
+                    }
+                }
+                else{
+                    if(str[i]==str[j]){
+                        //prefix subsequence count + suffix sum count+1
+
+                        dp[i][j] = 1+dp[i+1][j]+dp[i][j-1];
+                    }
+
+                    else{
+                        //prefix subsequence count + suffix sum count- subsequence count of middle
+                        dp[i][j] = dp[i][j-1]+dp[i+1][j]-dp[i+1][j-1];
+                    }
+                }
+                dp[i][j]%=mod;
+
+            }
+        }
+         if(dp[0][n-1]<0)return dp[0][n-1]+mod;
+        else return dp[0][n-1]%mod;
+    }
+
+};
+
+//{ Driver Code Starts.
+// Driver program
+int main()
+{
+    int t;
+    cin>>t;
+    while(t--)
+    {
+        string str;
+        cin>>str;
+        Solution ob;
+        long long int ans = ob.countPS(str);
+        cout<<ans<<endl;
+    } 
+}
+// } Driver Code Ends