3598: Reconnaissance
题目描述
According to the regulations of Berland's army, a reconnaissance unit should consist of exactly two soldiers. Since these two soldiers shouldn't differ much, their heights can differ by at most d centimeters. Captain Bob has n soldiers in his detachment. Their heights are a1,a2,...,an centimeters. Some soldiers are of the same height. Bob wants to know, how many ways exist to form a reconnaissance unit of two soldiers from his detachment.
Ways (1,2) and (2,1) should be regarded as different.
The first line contains two integers n and d (1≤n≤1000,1≤d≤109) − amount of soldiers in Bob's detachment and the maximum allowed height difference respectively. The second line contains n space-separated integers − heights of all the soldiers in Bob's detachment. These numbers don't exceed 109.
Output one number − amount of ways to form a reconnaissance unit of two soldiers, whose height difference doesn't exceed d.
5 10
10 20 50 60 65
6
5 1
55 30 29 31 55
6