codeforces 621B 对角线计数

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#include <iostream>#include <algorithm>#include <cstring> #include <vector>#include <cstdio>#include <cmath>using namespace std;typedef long long ll;const int N=2e3+20;int f[N],s[N];int main(){int n;cin>>n;memset(f,0,sizeof(f));memset(s,0,sizeof(s));while(n--){int x,y;cin>>x>>y;f[x+y]++;//x+y相等的点在副对角线上s[x-y+1000]++;// x-y相等的点在主对角线上 }ll ans=0;for(int i=0;i<=2000;i++){//对角线上有n个点 两两互相攻击的有C(n,2)个ans+=f[i]*(f[i]-1)/2;ans+=s[i]*(s[i]-1)/2;}if(ans<0)ans=0;cout<<ans<<endl;return 0;}