题目链接：http://codeforces.com/problemset/problem/251/A
Little Petya likes points a lot. Recently his mom has presented him n points lying on the line OX. Now Petya is wondering in how many ways he can choose three distinct points so that the distance between the two farthest of them doesn‘t exceed d.
Note that the order of the points inside the group of three chosen points doesn‘t matter.
The first line contains two integers: n and d (1?≤?n?≤?105; 1?≤?d?≤?109). The next line contains n integers x1,?x2,?...,?xn, their absolute value doesn‘t exceed 109 — the x-coordinates of the points that Petya has got.
It is guaranteed that the coordinates of the points in the input strictly increase.
Print a single integer — the number of groups of three points, where the distance between two farthest points doesn‘t exceed d.
Please do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, cout streams or the %I64dspecifier.
4 3 1 2 3 4
4
4 2 -3 -2 -1 0
2
5 19 1 10 20 30 50
1
In the first sample any group of three points meets our conditions.
In the seconds sample only 2 groups of three points meet our conditions: {-3, -2, -1} and {-2, -1, 0}.
In the third sample only one group does: {1, 10, 20}.
题意：
给出n和k，然后给出一个大小为 n 的集合，从集合中取出3个数，
最大数与最小数的差值小于k的方式有多少种。
代码如下：
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
using namespace std;
#define LL __int64
int main()
{
int n;
LL d;
LL a[100047];
while(~scanf("%d%I64d",&n,&d))
{
for(int i = 0; i < n; i++)
{
scanf("%I64d",&a[i]);
}
LL ans = 0;
for(int i = 1; i < n; i++)
{
LL tt = i-(lower_bound(a,a+i,a[i]-d)-a)-1;
ans+=tt*(tt+1)/2;//C n 2
}
printf("%I64d\n",ans);
}
return 0;
}
/*
4 3
1 2 3 4
4 2
-3 -2 -1 0
5 19
1 10 20 30 50
*/版权声明：本文为博主原创文章，未经博主允许不得转载。
CodeForces 251A. Points on Line（数学 lower_bound ）
原文：http://blog.csdn.net/u012860063/article/details/46793527