CodeForces - 651C

 1 #include <bits/stdc++.h>
 2 #define ll long long
 3 using namespace std;
 4 typedef pair<int,int> P;
 5 map<int,int> xx,yy;
 6 map<P,int> s;
 7 map<int,int>::iterator it1;
 8 map<P,int>::iterator it2;
 9 int main(){
10     int n;
11     scanf("%d",&n);
12     for(int i = 1; i <= n; i ++){
13         int a,b;
14         scanf("%d%d",&a,&b);
15         xx[a]++;yy[b]++;
16         s[P(a,b)]++;
17     }
18     ll ans = 0;
19     for(it1 = xx.begin(); it1!=xx.end(); it1++){
20         ans += (ll)(*it1).second*((*it1).second-1)/2;
21     }
22     for(it1 = yy.begin(); it1!=yy.end(); it1++){
23         ans += (ll)(*it1).second*((*it1).second-1)/2;
24     }
25     for(it2 = s.begin(); it2!=s.end(); ++it2){
26         ans -= (ll)(*it2).second*((*it2).second-1)/2;
27     }
28     cout << ans << endl;
29     return 0;
30 }