1208. Get Equal Substrings Within Budget

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.

Rust Solution

struct Solution;

impl Solution {
    fn equal_substring(s: String, t: String, max_cost: i32) -> i32 {
        let s: Vec<char> = s.chars().collect();
        let t: Vec<char> = t.chars().collect();
        let n = s.len();
        let mut cost: Vec<i32> = vec![0; n];
        for i in 0..n {
            cost[i] = (s[i] as i32 - t[i] as i32).abs();
        }
        let mut start = 0;
        let mut end = 0;
        let mut res = 0;
        let mut sum = 0;
        while end < n {
            if sum <= max_cost {
                sum += cost[end];
                end += 1;
            } else {
                sum -= cost[start];
                start += 1;
            }
            if sum <= max_cost {
                res = res.max(end - start);
            }
        }
        res as i32
    }
}

#[test]
fn test() {
    let s = "abcd".to_string();
    let t = "cdef".to_string();
    let max_cost = 3;
    let res = 1;
    assert_eq!(Solution::equal_substring(s, t, max_cost), res);
    let s = "abcd".to_string();
    let t = "acde".to_string();
    let max_cost = 0;
    let res = 1;
    assert_eq!(Solution::equal_substring(s, t, max_cost), res);
}

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