Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
Find the Celebrity in C++
Suppose we have n people (labeled from 0 to n - 1) and among them, there may exist one celebrity. We can say a person x is a celebrity when all the other n - 1 people know x but x does not know any of them. Here we have to find who the celebrity is or verify that there is not one.
We are allowed to ask only one question to person ‘A’, that "Hi, A. Do you know B?" to get information of whether A knows B or not. We have to ask minimum number of questions tofind out the celebrity. There is a list of lists as input called graph, the graph[i,j] = 1 when ith person knows jth person, otherwise 0.
So, if the input is like graph = [[1,1,0],[0,1,0],[1,1,1]],
then the output will be 1, as the celebrity is the person labeled as 1 because both 0 and 2 know him but 1 does not know anybody.
To solve this, we will follow these steps −
Define a function knows(), this will take a, b,
return true when graph[a, b] is true
From the main method do the following −
Define one stack st
for initialize i := 0, when i < n, update (increase i by 1), do −
insert i into st
while size of st > 1, do −
x := top element of st
delete element from st
y := top element of st
delete element from st
if knows(x, y) is true then, then −
insert y into st
Otherwise
insert x into st
x := top element of st
for initialize i := 0, when i < n, update (increase i by 1), do −
if i is same as x, then −
Ignore following part, skip to the next iteration
if knows(x, i) is true or knows(i, x) is false, then −
return -1
return x
Example
Let us see the following implementation to get a better understanding −
#include <bits/stdc++.h>
using namespace std;
class Solution {
vector<vector<int<> graph;
public:
Solution(vector<vector<int<> &graph){
this->graph = graph;
}
bool knows(int a, int b){
return graph[a][b];
}
int findCelebrity(int n) {
stack<int< st;
for (int i = 0; i < n; i++) {
st.push(i);
}
while (st.size() > 1) {
int x = st.top();
st.pop();
int y = st.top();
st.pop();
if (knows(x, y)) {
st.push(y);
}
else {
st.push(x);
}
}
int x = st.top();
for (int i = 0; i < n; i++) {
if (i == x)
continue;
if (knows(x, i) || !knows(i, x)) {
return -1;
}
}
return x;
}
};
main(){
vector<vector<int<> v = {{1,1,0},{0,1,0},{1,1,1}};
Solution ob(v);
cout << (ob.findCelebrity(3));
}Input
{{1,1,0},{0,1,0},{1,1,1}}
3Output
1
82 Views
