P1102 A-B 数对

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#include<bits/stdc++.h>
using namespace std;const int N=2e5+10;
int n,c;
int a[N];int main()
{ios::sync_with_stdio(0),cin.tie(0);cin>>n>>c;for(int i=1;i<=n;i++){cin>>a[i];}sort(a+1,a+n+1);int l=1,r=1;long long ans=0;for(int i=1;i<=n;i++){int A=a[i]+c;while(l<=n&&a[l]<A) l++;while(r<=n&&a[r]<=A) r++;ans+=r-l;}cout<<ans<<endl;return 0;
}