Minimum Substring Partition of Equal Character Frequency
<p>Given a string <code>s</code>, you need to partition it into one or more <strong>balanced</strong> <span data-keyword="substring">substrings</span>. For example, if <code>s == &quot;ababcc&quot;</code> then <code>(&quot;abab&quot;, &quot;c&quot;, &quot;c&quot;)</code>, <code>(&quot;ab&quot;, &quot;abc&quot;, &quot;c&quot;)</code>, and <code>(&quot;ababcc&quot;)</code> are all valid partitions, but <code>(&quot;a&quot;, <strong>&quot;bab&quot;</strong>, &quot;cc&quot;)</code>, <code>(<strong>&quot;aba&quot;</strong>, &quot;bc&quot;, &quot;c&quot;)</code>, and <code>(&quot;ab&quot;, <strong>&quot;abcc&quot;</strong>)</code> are not. The unbalanced substrings are bolded.</p>

<p>Return the <strong>minimum</strong> number of substrings that you can partition <code>s</code> into.</p>

<p><strong>Note:</strong> A <strong>balanced</strong> string is a string where each character in the string occurs the same number of times.</p>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;fabccddg&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">3</span></p>

<p><strong>Explanation:</strong></p>

<p>We can partition the string <code>s</code> into 3 substrings in one of the following ways: <code>(&quot;fab, &quot;ccdd&quot;, &quot;g&quot;)</code>, or <code>(&quot;fabc&quot;, &quot;cd&quot;, &quot;dg&quot;)</code>.</p>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;abababaccddb&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">2</span></p>

<p><strong>Explanation:</strong></p>

<p>We can partition the string <code>s</code> into 2 substrings like so: <code>(&quot;abab&quot;, &quot;abaccddb&quot;)</code>.</p>
</div>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
	<li><code>s</code> consists only of English lowercase letters.</li>
</ul>
Hash Table; String; Dynamic Programming; Counting
function minimumSubstringsInPartition(s: string): number {
    const n = s.length;
    const f: number[] = Array(n).fill(-1);
    const dfs = (i: number): number => {
        if (i >= n) {
            return 0;
        }
        if (f[i] !== -1) {
            return f[i];
        }
        const cnt: Map<number, number> = new Map();
        const freq: Map<number, number> = new Map();
        f[i] = n - i;
        for (let j = i; j < n; ++j) {
            const k = s.charCodeAt(j) - 97;
            if (freq.has(cnt.get(k)!)) {
                freq.set(cnt.get(k)!, freq.get(cnt.get(k)!)! - 1);
                if (freq.get(cnt.get(k)!) === 0) {
                    freq.delete(cnt.get(k)!);
                }
            }
            cnt.set(k, (cnt.get(k) || 0) + 1);
            freq.set(cnt.get(k)!, (freq.get(cnt.get(k)!) || 0) + 1);
            if (freq.size === 1) {
                f[i] = Math.min(f[i], 1 + dfs(j + 1));
            }
        }
        return f[i];
    };
    return dfs(0);
}
