Geeks4Geeks celebrity problem

TheCelebrityProblem.java

class GfG
{
    // The task is to complete this function
    int getId(int M[][], int n)
    {
       
        java.util.Stack<Integer> stack= new java.util.Stack<Integer>();
        // Your code here
        for(int i=0; i<n; i++){
            stack.push(i);
        }
        int a= stack.pop();
        int b= stack.pop();
        while(stack.size()>01){
            
            if(knows(M,a,b)){
                a=stack.pop();
            }else{
                b=stack.pop();
            }
        }
        int c=stack.pop();
        if(knows(M,a,b) && !knows(M,b,a)){
            c=b;
        }else if(knows(M,b,a) && !knows(M,a,b)){
            c=a;
        }
        for(int i=0; i<n; i++){
            if(i!=c){
                if(knows(M,c,i)|| !knows(M,i,c)){
                    return -1;
                }
            }
        }
        return c;
    }
    boolean knows(int [][] M, int a, int b){
        return M[a][b]==1;
    }
}