Number of Ways to Split a String
<p>Given a binary string <code>s</code>, you can split <code>s</code> into 3 <strong>non-empty</strong> strings <code>s1</code>, <code>s2</code>, and <code>s3</code> where <code>s1 + s2 + s3 = s</code>.</p>

<p>Return the number of ways <code>s</code> can be split such that the number of ones is the same in <code>s1</code>, <code>s2</code>, and <code>s3</code>. Since the answer may be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>

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

<pre>
<strong>Input:</strong> s = &quot;10101&quot;
<strong>Output:</strong> 4
<strong>Explanation:</strong> There are four ways to split s in 3 parts where each part contain the same number of letters &#39;1&#39;.
&quot;1|010|1&quot;
&quot;1|01|01&quot;
&quot;10|10|1&quot;
&quot;10|1|01&quot;
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;1001&quot;
<strong>Output:</strong> 0
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;0000&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> There are three ways to split s in 3 parts.
&quot;0|0|00&quot;
&quot;0|00|0&quot;
&quot;00|0|0&quot;
</pre>

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

<ul>
	<li><code>3 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>s[i]</code> is either <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
</ul>
Math; String
class Solution:
    def numWays(self, s: str) -> int:
        def find(x):
            t = 0
            for i, c in enumerate(s):
                t += int(c == '1')
                if t == x:
                    return i

        cnt, m = divmod(sum(c == '1' for c in s), 3)
        if m:
            return 0
        n = len(s)
        mod = 10**9 + 7
        if cnt == 0:
            return ((n - 1) * (n - 2) // 2) % mod
        i1, i2 = find(cnt), find(cnt + 1)
        j1, j2 = find(cnt * 2), find(cnt * 2 + 1)
        return (i2 - i1) * (j2 - j1) % (10**9 + 7)
