算法
(数学) $O(t)$
若 $\frac{k(k + 1)}{2} \leqslant s \leqslant \frac{(2n-k+1)k}{2}$,则答案为 Yes
,否则答案为 No
C++ 代码
#include <bits/stdc++.h>
using std::cin;
using std::cout;
using ll = long long;
int main() {
int t;
cin >> t;
while (t--) {
int n, k;
ll s;
cin >> n >> k >> s;
ll s1 = 1ll * (1 + k) * k / 2;
ll s2 = 1ll * (2 * n - k + 1) * k / 2;
if (s < s1 or s > s2) puts("No");
else puts("Yes");
}
return 0;
}