2021. Costume Party

单点时限: 2.0 sec

内存限制: 256 MB

It’s Halloween! Farmer John is taking the cows to a costume party,but unfortunately he only has one costume. The costume fits precisely two cows with a length of S (1 <= S <= 1,000,000). FJ has N cows(2 <= N <= 20,000) conveniently numbered 1..N; cow i has length L_i

(1 <= L_i <= 1,000,000). Two cows can fit into the costume if the sum of their lengths is no greater than the length of the costume.FJ wants to know how many pairs of two distinct cows will fit into the costume.

输入格式

  • Line 1: Two space-separated integers: N and S

  • Lines 2..N+1: Line i+1 contains a single integer: L_i

输出格式

  • Line 1: A single integer representing the number of pairs of cows FJcan choose. Note that the order of the two cows does not matter.

样例

Input
4 6
3
5
2
1
Output
4
OUTPUT DETAILS:
The four pairs are as follows: cow 1 and cow 3; cow 1 and cow 4; cow 2 and cow 4; and finally cow 3 and cow 4.

78 人解决,98 人已尝试。

149 份提交通过,共有 320 份提交。

3.2 EMB 奖励。

创建: 12 年,10 月前.

修改: 3 年,3 月前.

最后提交: 4 月前.

来源: USACO

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