celebrity problem

/*
You are in a party of N people, where only one person is known to everyone. Such a person may be present in the party, if yes, (s)he 
doesn’t know anyone in the party. Your task is to find the stranger (celebrity) in party.You will be given a square matrix M[][] where if
an element of row i and column j  is set to 1 it means ith person knows jth person. You need to complete the function getId() which finds 
the id of the celebrity if present else return -1. The function getId() takes two arguments, the square matrix M and its size N.

Note: Expected time complexity is O(N) with constant extra space.

Input:
The first line of input contains an element T denoting the number of test cases. Then T test cases follow. Each test case consist of 2 
lines. The first line of each test case contains a number denoting the size of the matrix M. Then in the next line are space separated 
values of the matrix M.

Output:
For each test case output will be the id of the celebrity if present (0 based index). Else -1 will be printed.

User Task:
The task is to complete the function getId() which returns the Id of celebrity if present, else -1.

Constraints:
1 <= T <= 50
2 <= N <= 501
0 <= M[][] <= 1

Example:
Input (To be used only for expected output) :
2
3
0 1 0 0 0 0 0 1 0
2
0 1 1 0

Output :
1
-1

Explanation :
For the above test case the matrix will look like
0 1 0 
*/

bool knows(int a[MAX][MAX] , int i, int j){
    return a[i][j]==1? true: false;
}

int getId(int a[MAX][MAX], int n)
{
     int candidate=0;
     for(int i=1; i<n&&candidate<n-1; i++){
         if(knows(a,candidate,i)){
             candidate=i;
         }
     }
     for(int k=0; k<n; k++){
         if(k!=candidate && (!knows(a,k,candidate) || knows(a,candidate,k))){
             return -1;
         }
     }
    return candidate;
}
0 0 0
0 1 0
Here,  the celebrity is the person with index 1 ie id 1