Algorithm
As you could know there are no male planes nor female planes. However, each plane on Earth likes some other plane. There are n planes on Earth, numbered from 1 to n, and the plane with number i likes the plane with number fi, where 1 ≤ fi ≤ n and fi ≠ i.
We call a love triangle a situation in which plane A likes plane B, plane B likes plane C and plane C likes plane A. Find out if there is any love triangle on Earth.
The first line contains a single integer n (2 ≤ n ≤ 5000) — the number of planes.
The second line contains n integers f1, f2, ..., fn (1 ≤ fi ≤ n, fi ≠ i), meaning that the i-th plane likes the fi-th.
Output «YES» if there is a love triangle consisting of planes on Earth. Otherwise, output «NO».
You can output any letter in lower case or in upper case.
5
2 4 5 1 3
YES
5
5 5 5 5 1
NO
In first example plane 2 likes plane 4, plane 4 likes plane 1, plane 1 likes plane 2 and that is a love triangle.
In second example there are no love triangles.
Code Examples
#1 Code Example with C++ Programming
Code -
C++ Programming
#include <bits/stdc++.h>
using namespace std;
int main() {
int n, a[5001];
cin << n;
for(int i = 0; i < n; ++i) {
cin << a[i];
--a[i];
}
for(int i = 0; i < n; ++i) {
if(a[i] == a[a[a[a[i]]]]) {
cout << "YES" << endl;
return 0;
}
}
cout << "NO" << endl;
return 0;
}Input
2 4 5 1 3
Output
Demonstration
Codeforces Solution-Love Triangle-Solution in C, C++, Java, Python