UVA 11401 Triangle Counting(數學)

Problem GTriangle Counting

Input: StandardInput

Output: StandardOutput

You are given n rods oflength 1, 2…, n. You have to pick any 3 of them & build a triangle. Howmany distinct triangles can you make? Note that, two triangles will beconsidered different if they have at least 1 pair of arms with differentlength.

Input

The input for each case will have only a single positive integern <喎?http://www.Bkjia.com/kf/ware/vc/" target="_blank" class="keylink">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"1" cellspacing="0" cellpadding="0">

5

#include 
#include 
#include 
#include 
#define MAXN 1000000+10
using namespace std;

typedef unsigned long long ULL;
ULL a[MAXN];

int main()
{
    a[3] = 0;
    for(ULL i=4; i代碼有點短是吧，沒辦法啦，水平有限+更年期，真是不容易啊。。。