Begin-End

Problem Statement

You are given a function f(x), where f(x) is 1 if the first and last characters of string x are equal; else it is 0.
You are given a string S and you have to find the sum of f(x) for all substrings x of given string S.

Note: A substring is a contiguous slice of string S[i:j] such that i≤j. It is a contiguous slice of the original string.

Input Format
The first line contains an integer N, length of S.
The second line contains a string S. S will contain only lower case characters (a−z).

Constraints
1≤|S|≤106
1≤|x|

Output Format
Print the required answer.

Sample Input

7
ababaca

Sample Output

14

Explanation
f("a")=1 , f("aba")=1 , f(“abaca”)=1 but f(“ab”)=0 , (“bac”)=0. Hence counting all substrings we get 14
The 14 substring are
a - 4(times)
b - 2
c - 1
aba - 2
bab - 1
aca - 1
ababa - 1
abaca - 1 

ababaca - 1


#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

int main() {
     long int input,i,hash[26]={0},ans=0;
    scanf("%ld",&input);
    char a[input];
    scanf("%s",a);
    for(i=0;i<input;i++)
        {
        hash[(int)a[i]-97]++;
    }
    for(i=0;i<26;i++)
        {
        if(a[i]>0)
            {
            ans=ans+((hash[i]*(hash[i]+1))/2);
        }
    }
    printf("%ld",ans);
    return 0;
}