Problem link
Author: @maazbinasad3
Tester: @prasoonjain006
Editorialist: @maazbinasad3
Difficulty: Cakewalk
Prerequisites : Sequences and Series
Problem
Find the Nth term of given sequence 1,3,6… so on.
Observation 1
This sequence is the triangular numbers.
Observation 2
The Nth term represents sum of first n natural numbers given by (n*(n+1))/2.
Solution
Setter’s solution
#include<iostream>
#include<unordered_map>
#include<algorithm>
#include<stack>
#pragma GCC optimize("O2")
typedef long long int ll;
using namespace std;
int main(){
ll test;
cin>>test;
while(test--){
ll n;
cin>>n;
cout<<(n*(n+1))/2<<"\n";
}
}