1321. Get Equal Substrings Within Budget

• Difficulty: Medium

• Topics: Array, Sliding Window

• Similar Questions:

Problem:

You are given two strings s and t of the same length. You want to change s to t. Changing the i-th character of s to i-th character of t costs |s[i] - t[i]| that is, the absolute difference between the ASCII values of the characters.

You are also given an integer maxCost.

Return the maximum length of a substring of s that can be changed to be the same as the corresponding substring of twith 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.

Example 1:

Input: s = "abcd", t = "bcdf", maxCost = 3
Output: 3
Explanation: "abc" of s can change to "bcd". That costs 3, so the maximum length is 3.

Example 2:

Input: s = "abcd", t = "cdef", maxCost = 3
Output: 1
Explanation: Each character in s costs 2 to change to charactor in t, so the maximum length is 1.

Example 3:

Input: s = "abcd", t = "acde", maxCost = 0
Output: 1
Explanation: You can't make any change, so the maximum length is 1.

Constraints:

• 1 <= s.length, t.length <= 10^5
• 0 <= maxCost <= 10^6
• s and t only contain lower case English letters.

Solutions:

class Solution {
public:
    int equalSubstring(string s, string t, int maxCost) {
        int len = 0;
        int cost = 0;

        if (maxCost < 0)    return 0;

        int left = 0;
        for (int right = 0; right < s.length(); ++right) {
            cost += abs(t[right] - s[right]);
            while (cost > maxCost) {
                cost -= abs(t[left] - s[left]);
                ++left;
            }
            len = max(len, right - left + 1);
        }

        return len;
    }
};