UVa - 11401 - Triangle Counting.cpp

#include<bits/stdc++.h>
#define DIST(x1,x2, y1, y2) (((x1-x2)*(x1-x2))+((y1-y2)*(y1-y2)))
#define DIST3D(x1,x2, y1, y2, z1, z2) (((x1-x2)*(x1-x2))+((y1-y2)*(y1-y2)) + ((z1-z2)*(z1-z2)))
#define CLR(a) a.clear()
#define VCLR(a, n) for(int i=0; i<=n+3; i++) a[i].clear()
#define SIZE(a) a.size()
#define ERASE(a, b) memset(a, b, sizeof a)
#define PB(a, b) a.push_back(b)
#define PB2(a,i,b) a[i].push_back(b)
#define LL long long
#define DBG cout<<"I Am Here"<<endl
#define DBGA(a) cout<<a<<endl
#define DBGI(b,a) cout<<b<<' '<<a<<endl
#define DBGL(i,s,e,b) or(int i=s; i<=e; i++) cout<<b<<endl
#define INF 1e9
#define INV 1e-6
#define sll(a) scanf("%I64d", &a)
#define pll(a) printf("%I64d\n", a)
#define si(a) scanf("%d", &a)
#define pii pair<int,int>
#define MAX 100006
#define CASE(i) printf("Case %d:\n", i);
#define PI acos(-1)
#define piis pair<int, string>
#define fast1 ios_base::sync_with_stdio(false);
#define fast2 cin.tie(0)

using namespace std;

LL F[1000007], P[1000007];

void precal()
{
    F[3] = 0; P[3] = 0;
    LL var = 0;
    for(int i=4; i<=1000000; i++)
    {
        if(i%2==0)
        {
            var++;
            P[i] = P[i-1] + var;
            F[i] = F[i-1] + P[i];
        }
        else
        {
            P[i] = P[i-1] + var;
            F[i] = F[i-1] + P[i];
        }
    }
}

int main()
{
    precal();
    int n;
    while(scanf("%d", &n) && n>=3)
    {
        printf("%lld\n", F[n]);
    }
}