题解 | 数对计数

import sys
n,c=list(map(int,input().split()))
arr=list(map(int,input().split()))
dic={}
for i in arr:
    dic[i]=dic.get(i,0)+1
lis=set(dic.keys())
res=0
for i in lis:
    target=i+c
    if target in lis:
        res+=dic[i]*dic[target]
print(res)