---
# System prepended metadata

title: Get Equal Substrings Within Budget
tags: [data_structure_python]

---

---
tags: data_structure_python
---

# 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 `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 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.
```

# Solution

### Solution 1: Sliding window (Dynamic)

```python=
class Solution:
    def equalSubstring(self, s: str, t: str, maxCost: int) -> int:
        # Time complexity: O(n).
        # Space complexity: O(1).
        beg, end, m = 0, 0, len(s)
        cost, maxi = 0, 0
        
        while end < m:
            
            cost += abs(ord(s[end]) - ord(t[end]))
                        
            while cost > maxCost:
                cost -= abs(ord(s[beg]) - ord(t[beg]))
                beg += 1
            
            maxi = max(maxi, end-beg+1)    
            end += 1
            
        return maxi
```