added the celebrity problem

stack_problems/the_celebrity_problem.cpp

@@ -0,0 +1,66 @@
+//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.
+
+//SOLUTION
+#include<bits/stdc++.h>
+using namespace std;
+#define MAX 501
+int getId(int M[MAX][MAX],int n);
+int main()
+{
+    int T;
+    cin>>T;
+    int M[MAX][MAX];
+    while(T--)
+    {
+        int N;
+        cin>>N;
+        memset(M,0,sizeof M);
+        for(int i=0;i<N;i++)
+        {
+            for(int j=0;j<N;j++)
+            {
+                cin>>M[i][j];
+            }
+        }
+        cout<<getId(M,N)<<endl;
+    }
+}
+
+
+
+int getId(int M[MAX][MAX], int n)
+{
+    stack<int>s;
+    for(int i=0;i<n;i++){
+        s.push(i);
+    }
+    while(s.size()>1){
+        int A=s.top();
+        s.pop();
+        int B=s.top();
+        s.pop();
+        if(M[A][B]==1){
+            s.push(B);
+        }
+        else{
+            s.push(A);
+        }
+    }
+    int C=s.top();
+    s.pop();
+    for(int i=0;i<n;i++){
+        if((M[C][i]==1||M[i][C]==0)&&i!=C){
+            return -1;
+        }
+    }
+
+    return C;
+
+}