<p>You are given two strings <code>s</code> and <code>t</code> of the same length and an integer <code>maxCost</code>.</p>

<p>You want to change <code>s</code> to <code>t</code>. Changing the <code>i<sup>th</sup></code> character of <code>s</code> to <code>i<sup>th</sup></code> character of <code>t</code> costs <code>|s[i] - t[i]|</code> (i.e., the absolute difference between the ASCII values of the characters).</p>

<p>Return <em>the maximum length of a substring of </em><code>s</code><em> that can be changed to be the same as the corresponding substring of </em><code>t</code><em> with a cost less than or equal to </em><code>maxCost</code>. If there is no substring from <code>s</code> that can be changed to its corresponding substring from <code>t</code>, return <code>0</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;abcd&quot;, t = &quot;bcdf&quot;, maxCost = 3
<strong>Output:</strong> 3
<strong>Explanation:</strong> &quot;abc&quot; of s can change to &quot;bcd&quot;.
That costs 3, so the maximum length is 3.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;abcd&quot;, t = &quot;cdef&quot;, maxCost = 3
<strong>Output:</strong> 1
<strong>Explanation:</strong> Each character in s costs 2 to change to character in t,  so the maximum length is 1.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;abcd&quot;, t = &quot;acde&quot;, maxCost = 0
<strong>Output:</strong> 1
<strong>Explanation:</strong> You cannot make any change, so the maximum length is 1.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>t.length == s.length</code></li>
	<li><code>0 &lt;= maxCost &lt;= 10<sup>6</sup></code></li>
	<li><code>s</code> and <code>t</code> consist of only lowercase English letters.</li>
</ul>

class Solution:
    def calculate_cost(self, ch1, ch2):
        return abs(ord(ch1) - ord(ch2))

    def equalSubstring(self, s: str, t: str, maxCost: int) -> int:
        left = ans = curr_cost = 0

        for right in range(len(s)):
            cost = self.calculate_cost(s[right], t[right])
            curr_cost += cost

            while curr_cost > maxCost:
                left_cost = self.calculate_cost(s[left], t[left])
                curr_cost -= left_cost
                left += 1

            ans = max(ans, right - left + 1)

        return ans

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