Sanket and strings challenge

#1

#include<bits/stdc++.h>
using namespace std;

int main(){
int k;
cin>>k;
string str;
cin>>str;
int ans=0;
int count[]={0,0};
int l=0;
for(int r=0;r<str.length();r++){
char a = str[r];
count[a - ‘a’]++;
if(min(count[0], count[1]) > k){
count[str[l] - ‘a’]–;
l++;
}
else
ans++;
}
cout<<ans;
return 0;
}

I read this code in doubts regarding this challenge.I am not able to understand the logic behind it.Please explain it.

#2

This code is showing compilation error.
In this question as there are only two characters in the string,so if we have to consider max length of string a possible with atmost k changes and similarly for b.
You can make two seperate functions one which checks max length possible for string a while other for string b.