1208. Get Equal Substrings Within Budget

Description

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.

 

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.

 

Solutions

Solution: Sliding Window

• Time complexity: O(n)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {string} s
 * @param {string} t
 * @param {number} maxCost
 * @return {number}
 */
const equalSubstring = function (s, t, maxCost) {
  let left = 0;
  let cost = 0;
  let result = 0;

  for (let index = 0; index < s.length; index++) {
    const needCost = Math.abs(s.charCodeAt(index) - t.charCodeAt(index));

    cost += needCost;
    while (cost > maxCost && left <= index) {
      cost -= Math.abs(s.charCodeAt(left) - t.charCodeAt(left));
      left += 1;
    }
    result = Math.max(index - left + 1, result);
  }
  return result;
};