#### 原题说明

In a town, there are `N` people labelled from `1` to `N`. There is a rumor that one of these people is secretly the town judge.

If the town judge exists, then:

1. The town judge trusts nobody.
2. Everybody (except for the town judge) trusts the town judge.
3. There is exactly one person that satisfies properties 1 and 2.
You are given trust, an array of pairs `trust[i] = [a, b]` representing that the person labelled a trusts the person labelled `b`.

If the town judge exists and can be identified, return the label of the town judge. Otherwise, return `-1`.

Example 1:

Input: `N = 2, trust = [[1,2]]`
Output: `2`

Example 2:

Input: `N = 3, trust = [[1,3],[2,3]]`
Output: `3`

Example 3:

Input: `N = 3, trust = [[1,3],[2,3],[3,1]]`
Output: `-1`

Example 4:

Input: `N = 3, trust = [[1,2],[2,3]]`
Output: `-1`

Example 5:

Input: `N = 4, trust = [[1,3],[1,4],[2,3],[2,4],[4,3]]`
Output: `3`

Note:

1. `1 <= N <= 1000`
2. `trust.length <= 10000`
3. `trust[i]` are all different
4. `trust[i][0] != trust[i][1]`
5. `1 <= trust[i][0], trust[i][1] <= N`

#### 归纳总结

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