1234

class Solution {
public:
    int balancedString(string s) {
        unordered_map<char, int> count;
        int left, right, n=s.length(), k=n/4;

        for(int i=0; i<n; i++)
            count[s[i]]++;

        int ans = n;
        for(left=0, right=0; right<n; right++){
            count[s[right]]--;
            while(left<n && count['Q']<=k && count['W']<=k && count['E']<=k && count['R']<=k){
                ans = min(ans, right-left+1);
                count[s[left++]] += 1;
            }
        }
        return ans;
    }
};