CodeForces 621B Wet Shark and Bishops

记录一下每个对角线上有几个，然后就可以算了

#include<cstdio>
#include<cstring>
#include<cmath>
#include<ctime>
#include<vector>
#include<algorithm>
using namespace std;

const int maxn=2000+10;
int n;
long long w1[maxn];
long long w2[maxn];
long long ans;

int main()
{
    int n;
    scanf("%d",&n);
    ans=0;
    memset(w1,0,sizeof w1);
    memset(w2,0,sizeof w2);

    for(int i=1; i<=n; i++)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        int p=1000;

        p=p+(x-1);
        p=p-(y-1);

        w1[p]++;

        p=1000;
        p=p+x-1;
        p=p-(1000-y);
        w2[p]++;
    }

    for(int i=1; i<=1999; i++)
        if(w1[i]!=1&&w1[i]!=0)
            ans=ans+(w1[i]-1)*w1[i]/2;

    for(int i=1; i<=1999; i++)
        if(w2[i]!=1&&w2[i]!=0)
            ans=ans+(w2[i]-1)*w2[i]/2;

    printf("%lld\n",ans);

    return 0;
}