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A celebrity is a person who is known to all but does not know anyone at a party. If you go to a party of N people, find if there is a celebrity in the party or not.

A square NxN matrix M[][] is used to represent people at the party such that if an element of row i and column j is set to 1 it means ith person knows jth person. Here M[i][i] will always be 0.

**Note:** Follow 0 based indexing.

**Example 1:**

**Input:**
N = 3
M[][] = {{0 1 0},
{0 0 0},
{0 1 0}}
**Output:** 1
**Explanation: **0th and 2nd person both
know 1. Therefore, 1 is the celebrity.

**Example 2:**

**Input:**
N = 2
M[][] = {{0 1},
{1 0}}
**Output:** -1
**Explanation: **The two people at the party both
know each other. None of them is a celebrity.

**Your Task:**

You don't need to read input or print anything. Complete the function **celebrity()** which takes the matrix M and its size N as input parameters and returns the index of the celebrity. If no such celebrity is present, return -1.

**Expected Time Complexity:** O(N)

**Expected Auxiliary Space:** O(1)

**Constraints:**

2 <= N <= 3000

0 <= M[][] <= 1

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The Celebrity Problem

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