UVA 11401:Triangle Counting

简单规律题

#include<cstdio>
using namespace std;

typedef long long ll;
const int maxn=1000000+100;

ll f[maxn];

void slove(){
  
  f[3]=0;
  for(int i=4;i<maxn;i++) f[i]=f[i-1]+((ll)(i-1)*(i-2)/2-(i-1)/2)/2;
}

int main(){
  
  slove();
  int n;
  while(scanf("%d",&n)==1){
    
    if(n<3) break;
    printf("%lld\n",f[n]);
  }
}