1208. Get Equal Substrings Within Budget

Medium

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 i^th 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.

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 character in t, so the maximum length is 1.

Example 3:

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

Constraints:

1 <= s.length <= 10⁵
t.length == s.length
0 <= maxCost <= 10⁶
s and t consist of only lowercase English letters.

Solution:

class Solution {

    /**
     * @param String $s
     * @param String $t
     * @param Integer $maxCost
     * @return Integer
     */
    function equalSubstring($s, $t, $maxCost) {
        $j = 0;
        for ($i = 0; $i < strlen($s); ++$i) {
            $maxCost -= abs(ord($s[$i]) - ord($t[$i]));
            if ($maxCost < 0)
                $maxCost += abs(ord($s[$j]) - ord($t[$j++]));
        }

        return strlen($s) - $j;
    }
}

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