Kindly help with this question. It is telling to optimize the code

#1

https://practice.geeksforgeeks.org/problems/the-celebrity-problem/1/?track=SPC-Stack&batchId=154

class Celebrity
{
// The task is to complete this function
int getId(int M[][], int n)
{
Stack s=new Stack<>();
for(int i=0;i<n;i++)
{
s.push(i);
}
int a,b;

    while(s.size()>1){
        a=s.pop();
        
       b=s.pop();
        
        if(checkKnown(M,a,b))
            s.push(b);
        else    
            s.push(a);
    }
    
    int celeb= s.pop();
    for(int i=0;i<n;i++)
    {
        if((i!=celeb) && (checkKnown(M,celeb,i)) || (!checkKnown(M,i,celeb)))
            return -1;
    }
    return celeb;
}
boolean checkKnown(int M[][],int a,int b)
{
    return M[a][b]==1?true:false;
}

}