find-the-town-judge

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Algorithms

In a town, there are <code>n</code> people labeled from <code>1</code> to <code>n</code>. There is a rumor that one of these people is secretly the town judge.

If the town judge exists, then:

<ol>
	<li>The town judge trusts nobody.</li>
	<li>Everybody (except for the town judge) trusts the town judge.</li>
	<li>There is exactly one person that satisfies properties 1 and 2.</li>
</ol>

You are given an array <code>trust</code> where <code>trust[i] = [ai, bi]</code> representing that the person labeled <code>ai</code> trusts the person labeled <code>bi</code>. If a trust relationship does not exist in <code>trust</code> array, then such a trust relationship does not exist.

Return the label of the town judge if the town judge exists and can be identified, or return <code>-1</code> otherwise.

&nbsp;
Example 1:

<pre>
Input: n = 2, trust = [[1,2]]
Output: 2
</pre>

Example 2:

<pre>
Input: n = 3, trust = [[1,3],[2,3]]
Output: 3
</pre>

Example 3:

<pre>
Input: n = 3, trust = [[1,3],[2,3],[3,1]]
Output: -1
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= n &lt;= 1000</code></li>
	<li><code>0 &lt;= trust.length &lt;= 104</code></li>
	<li><code>trust[i].length == 2</code></li>
	<li>All the pairs of <code>trust</code> are unique.</li>
	<li><code>ai != bi</code></li>
	<li><code>1 &lt;= ai, bi &lt;= n</code></li>
</ul>