665C - Simple Strings - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;
int small[100005], big[100005];

int main()
{
    int result, len, cnt, i, j;
    string str, res="";
    char ch;
    cin>>str;
    len = str.length();

    for(i=0;i<len;i++){
//        printf("%d ",i);
        if(str[i]== str[i+1]){
            if(i+2<len){
                if(str[i] == 'z') ch = 'a';
                else ch = str[i]+1;
                while(1){
                    if(ch == 'z') ch = 'a';
                    if(str[i+2] != ch && str[i] != ch){
                        res += str[i];
                        res += ch;
                        i++;
                        break;
                    } else{
                        ch++;
                    }
                }
            }else {
//                printf("Else in 2nd level:\t");
                if(str[i] == 'z') ch = 'a';
                else ch = 'z';
                res += str[i];
                res += ch;
                i++;
                break;
            }
        }
        else{
            res += str[i];
        }
    }
  //  printf("\n");
    cout<<res;
}