UVA 11401 数学题
给1到n,n个不同的数,问能组成多少三角形
打表找规律得
#include<cstdio>
typedef long long ll;
const int maxn = 1000100;
ll a[maxn + 10];
int main(){
a[3] = 0;
for(int i = 4; i <= maxn; i++)
a[i] = a[i-1] + (i - 2) / 2;
ll n;
while(scanf("%lld", &n) == 1 && n >= 3)
printf("%lld\n", a[n]);
return 0;
}