P1102 A-B 数对(lower_bound函数)

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#include<bits/stdc++.h>
using namespace std;typedef long long LL;
const int N=2e5+10;
LL a[N];
LL c;
int n;int main()
{ios::sync_with_stdio(0),cin.tie(0);cin>>n>>c;for(int i=0;i<n;i++) cin>>a[i];sort(a,a+n);LL ans=0;for(int i=0;i<n;i++){LL A=a[i];LL target=A+c;int l=lower_bound(a,a+n,target)-a;int r=upper_bound(a,a+n,target)-a;ans+=(r-l);}cout<<ans<<endl;
}