Count all Palindrome Sub-Strings in a String in C++

In this tutorial, we will be discussing a program to find the number of palindrome sub strings in a string.

For this we will be given a string. Our task is to count the number of palindrome sub strings in the given string with length greater than 3.

Example

#include<bits/stdc++.h>
using namespace std;
//counting palindrome strings
int count_pstr(char str[], int n){
   int dp[n][n];
   memset(dp, 0, sizeof(dp));
   bool P[n][n];
   memset(P, false , sizeof(P));
   for (int i= 0; i< n; i++)
      P[i][i] = true;
   for (int i=0; i<n-1; i++) {
      if (str[i] == str[i+1]) {
         P[i][i+1] = true;
         dp[i][i+1] = 1 ;
      }
   }
   for (int gap=2 ; gap<n; gap++) {
      for (int i=0; i<n-gap; i++) {
         int j = gap + i;
         //if current string is palindrome
         if (str[i] == str[j] && P[i+1][j-1] )
            P[i][j] = true;
         if (P[i][j] == true)
            dp[i][j] = dp[i][j-1] + dp[i+1][j] + 1 - dp[i+1][j-1];
         else
            dp[i][j] = dp[i][j-1] + dp[i+1][j] - dp[i+1][j-1];
      }
   }
   return dp[0][n-1];
}
int main(){
   char str[] = "abaab";
   int n = strlen(str);
   cout << count_pstr(str, n) << endl;
   return 0;
}

Output

3

Ayush Gupta

Updated on 10-Feb-2020 11:13:53

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