HackerRank "Palindrome Index"

We compare two end' (current) chars and the key is how to check when there's a mismatch - DFS.

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <memory.h>
using namespace std;

bool isPalin(char *in, int i, int j)
{
    if (i == j) return true;    
    if (*(in + i) != *(in + j)) return false;
    else
    {
        if (i == j - 1) return true;
        else return isPalin(in, i + 1, j - 1);
    }
}
int main() {
    
    int cnt; cin >> cnt;
    while (cnt--)
    {
        char in[100006] = {0};
        cin >> in;
        size_t len = strlen(in);
        
        int ret = -1;
        int i = 0, j = len - 1;
        while (i < j)
        {
            if (in[i] == in[j])
            {
                i++; j--;
            }
            else
            {
                if (isPalin(in, i + 1, j))
                {
                    ret = i;
                    break;
                }
                else
                {
                    ret = j;
                    break;
                }
            }
        }
        cout << ret << endl;
    }
    return 0;
}