 # GRNDS - Editorial

https://www.codechef.com/GSCO2021/problems/GRDNS

Author: Akshit Panday
Tester: Rutuja Deshmukh
Editorialist: Sarthak Chafle

CAKEWALK

NONE

# PROBLEM:

We need to print the position of all the magical planets in the galaxy.

# QUICK EXPLANATION:

You are given a number that represents the number of planets in the galaxy and an array consisting of threat level of each planet, you have to print the position of all magical planets .

# EXPLANATION:

As per the given question a planet is stated as a magical planet if

1. its threat level is greater than that of the next planet
2. if the threat level of a planet and the threat level of the next planet has no common divisor than 1, i.e. their threat levels are coprime numbers or have GCD(Greatest Common Divisor) = 1.

we need to print the positions of all such planets, assuming that the planets are in a straight line and the galaxy has atleast 2 planets.
If no such planets exists we need to print “Wrong Signal”.

after following all the given conditions we can conclude that the last planet can never be magical.

COPRIME NUMBERS:
two integers a and b are coprime, relatively prime or mutually prime if the only positive integer that is a divisor of both of them is 1. Consequently, any prime number that divides one of a or b does not divide the other. This is equivalent to their greatest common divisor being 1

# SOLUTIONS:

Setter's Solution
``````   /* package codechef; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Codechef {

public static void main (String[] args) {
Scanner sc = new Scanner(System.in);
int testCases = sc.nextInt();
while( testCases --> 0) {
int N = sc.nextInt();
long[] arr = new long[N];
for(int i=0; i<arr.length; i++) {
arr[i] = sc.nextLong();
}

StringBuilder str = new StringBuilder();

boolean isExist = false;
for(int i=0; i<arr.length-1; i++) {
if(arr[i] > arr[i+1] && gcd(arr[i],arr[i+1]) == 1 ) {
//System.out.print(i+1 + " ");
int res = i+1;
str.append(res + " ");
isExist = true;
}
}
if(!isExist) System.out.println("Wrong Signal");
else System.out.println(String.valueOf(str));
}
sc.close();
}

static long gcd(long n1, long n2) {
if (n2 == 0) {
return n1;
}
return gcd(n2, n1 % n2);
}
}
``````
Tester's Solution
``````#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main(){
ll t;
cin>>t;
while(t--){
ll n;
cin>>n;
bool flg=0;
vector<ll>v(n),ans;
for(ll i=0;i<n;i++) cin>>v[i];
for(ll i=1;i<n;i++){
if(v[i-1]>v[i] and __gcd(v[i],v[i-1])==1 ){
cout<<i<<" ";
flg=1;
}
}
if(flg) cout<<"\n";
else cout<<"Wrong Signal\n";

}
return 0;
}
``````
Editorialist's Solution
``````#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);

#ifndef ONLINE_JUDGE
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
int t;
cin >> t;
while (t--) {
ll n;
cin >> n;
vector<ll> arr(n);
for (ll i = 0; i < n; i++) {
cin >> arr[i];
}
bool isExits = false;
for (ll i = 0; i < n - 1; i++) {
if (arr[i] > arr[i + 1] && __gcd(arr[i], arr[i + 1]) == 1) {
cout << i + 1 << " ";
isExits = true;
}
}
if (isExits == false) cout << "Wrong Signal";
cout << "\n";
}
return 0;
}
``````
3 Likes