#include <stdio.h>

int main() { int t; scanf("%d", &t);

while (t--) {
    long long n, k, x;
    scanf("%lld %lld %lld", &n, &k, &x);
    
    // 最小可能和：1+2+...+k
    long long min_sum = k * (k + 1) / 2;
    
    // 最大可能和：n+(n-1)+...+(n-k+1)
    long long max_sum = k * n - k * (k - 1) / 2;
    
    if (x >= min_sum && x <= max_sum) {
        printf("YES\n");
    } else {
        printf("NO\n");
    }
}

return 0;

}

C :

#include <stdio.h>
int main()
{
    long long t,n,k,x[110]={0},i,j,y,a[110],sum[110];
    scanf("%lld",&t);
    for(i=0;i<t;i++)
    {
    	sum[i]=y=0;
        scanf("%lld%lld%lld",&n,&k,&x[i]);
        for(j=0;j<k;j++)
        {
        	y=y+n-j;
        	sum[i]=sum[i]+j;
		}   
        a[i]=y;
    } 
    for(i=0;i<t;i++)
    {
    	if(a[i]>=x[i]&&sum[i]+k<=x[i])
         printf("YES");
        else
         printf("NO");
         printf("\n");
	}   
    return 0;
}

C++ :

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N=1e6+10;
typedef pair<int,int> PII;
typedef priority_queue<int , vector<int>, greater<int>> minqueue;  //从小到大 queue
typedef priority_queue<int, vector<int>, less<int>> maxqueue;      //从大到小 queue

int gcd(int a, int b){  //最大公因数 
    return b ? gcd(b, a % b) : a;
}

int lcm(int a, int b){ //最小公倍数 
    return a * b / __gcd(a, b);
}

int qmi(int base, int power, int p)  //快速幂求余 
{
	int result = 1;   
	while (power > 0)           
	{
		if (power & 1)         							
			result = result * base % p;   
		base = base * base % p ;       						
		power >>= 1;         						
	}
	return result % p;       
}

void solve()
{
	int n,k,x;
	cin>>n>>k>>x;
	int cnt1=0,cnt2=0;
	for(int i=1;i<=k;i++) cnt1+=i;
	for(int j=n;j>n-k;j--) cnt2+=j;
	if(cnt1<=x&&cnt2>=x) cout<<"YES"<<'\n';
	else cout<<"NO"<<'\n';
}

signed main()
{
	ios::sync_with_stdio(false); cin.tie(0); cout.tie(0);
	int t;
	t=1;
	cin>>t; 
	while(t--)     
	{
		solve();
	}
	return 0;
}