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Count all Palindromic Subsequence in a given String in C++
In this tutorial, we will be discussing a program to find the number of all palindromic subsequences in a given string.
For this we will be provided with a string. Our task is to find the number of palindromic subsequences that can be made in that given string.
Example
#include<iostream>
#include<cstring>
using namespace std;
//returning total palindromic sequence
int count_palin(string str){
int N = str.length();
//creating a 2D array
int cps[N+1][N+1];
memset(cps, 0 ,sizeof(cps));
for (int i=0; i<N; i++)
cps[i][i] = 1;
for (int L=2; L<=N; L++){
for (int i=0; i<N; i++){
int k = L+i-1;
if (str[i] == str[k])
cps[i][k] = cps[i][k-1] + cps[i+1][k] + 1;
else
cps[i][k] = cps[i][k-1] + cps[i+1][k] - cps[i+1][k-1];
}
}
return cps[0][N-1];
}
int main(){
string str = "abcb";
cout << "Total palindromic subsequence are : " << count_palin(str) << endl;
return 0;
}Output
Total palindromic subsequence are : 6
Updated on: 10-Feb-2020
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