//GPLT L2

GPLT L2"/>

//GPLT L2

1.STL
2.math
3.lower_bound和upper_bound的底层是二分实现的

#include<bits/stdc++.h>
using namespace std;
#define ll long long
ll a[200005];int main()
{ll n,v;scanf("%lld%lld",&n,&v);for(int i=0;i<n;i++)scanf("%lld",&a[i]);    ll ans=0;sort(a,a+n);for(int i=0;i<n;i++){ll x = a[i], y = v;//寻找z满足x+y>z , x+z > y ,y + z > x ,即 z<x+y 且 z > max(y-x,x-y) == abs(x-y)//每次搜索区间以当前区间为起点 避免重复//返回第一个>=x+y的值 则[i,r]为<x+y的zint r = lower_bound(a+1+i,a+n,x+y) - a;//返回第一个>abs(x-y)的值的下标 则[l,n]为>abs(x+y)的zll l = upper_bound(a+1+i,a+n,abs(x-y)) -a;ans += r -l;}cout<<ans;return 0;
}