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 `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 = 3Output:3Explanation:"abc" of s can change to "bcd". That costs 3, so the maximum length is 3.

**Example 2:**

Input:s = "abcd", t = "cdef", maxCost = 3Output:1Explanation: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 = 0Output:1Explanation: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.

```
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);
}
```