题解 | 数对计数

import java.util.*;
public class Main{
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        HashMap<Integer,Integer> map = new HashMap<>();
        int n = in.nextInt(),c = in.nextInt(),i=0;
        int[] a = new int[n];
        while(n-->0){
            int t = in.nextInt();
            map.put(t+c,map.getOrDefault(t+c,0)+1);
            a[i] = t;
            i++;
        }
        int ans = 0;
        for(int j=0;j<a.length;j++){
            int cur = map.getOrDefault(a[j],0);
            ans += cur;
        }
        System.out.println(ans);
    }
}