Get Equal Substrings Within Budget
<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>
String; Binary Search; Prefix Sum; Sliding Window
function equalSubstring(s: string, t: string, maxCost: number): number {
    const n = s.length;
    const f = Array(n + 1).fill(0);

    for (let i = 0; i < n; i++) {
        f[i + 1] = f[i] + Math.abs(s.charCodeAt(i) - t.charCodeAt(i));
    }

    const check = (x: number): boolean => {
        for (let i = 0; i + x - 1 < n; i++) {
            if (f[i + x] - f[i] <= maxCost) {
                return true;
            }
        }
        return false;
    };

    let l = 0,
        r = n;
    while (l < r) {
        const mid = (l + r + 1) >> 1;
        if (check(mid)) {
            l = mid;
        } else {
            r = mid - 1;
        }
    }

    return l;
}
