1208. Get Equal Substrings Within Budget

You are given two strings s and t of the same length and an integer maxCost.

You want to change s to t. Changing the ith character of s to ith character of t costs |s[i] - t[i]| (i.e., the absolute difference between the ASCII values of the characters).

Return the maximum length of a substring of s that can be changed to be the same as the corresponding substring of t with a cost less than or equal to maxCost. If there is no substring from s that can be changed to its corresponding substring from t, return 0.

class Solution {
public:
    int equalSubstring(string s, string t, int maxCost) {
        int res = 0, l = 0, r = 0, n = s.length(), sum = 0;
        
        while(r < n) {
            while(r < n and sum <= maxCost) {
                res = max(res, r - l);
                sum += abs(t[r] - s[r]);
                r++;
            }
            if(sum <= maxCost) res = max(res, r - l);
            
            while(sum > maxCost and l < r) {
                sum -= abs(t[l] - s[l]);
                l++;
            }
        }
        
        return res;
    }
};