Codeforces Round #345 (Div. 1) A. Watchmen

相同的X,Y计进去，相同的二元组(X,Y)去重。

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <cstring>
#include <set>
#include <map>
#include <list>
#include <queue>
#include <string>
#include <iostream>
#include <algorithm>
#include <functional>
#include <stack>
using namespace std;
typedef long long ll;
#define T int t_;Read(t_);while(t_--)
#define dight(chr) (chr>='0'&&chr<='9')
#define alpha(chr) (chr>='a'&&chr<='z')
#define INF (0x3f3f3f3f)
#define maxn (200005)
#define hashmod 100000007
#define ull unsigned long long
#define repne(x,y,i) for(i=x;i<y;++i)
#define repe(x,y,i) for(i=x;i<=y;++i)
#define ri register int
void Read(int &n){char chr=getchar(),sign=1;for(;!dight(chr);chr=getchar())if(chr=='-')sign=-1;
    for(n=0;dight(chr);chr=getchar())n=n*10+chr-'0';n*=sign;}
void Read(ll &n){char chr=getchar(),sign=1;for(;!dight(chr);chr=getchar())if
    (chr=='-')sign=-1;
    for(n=0;dight(chr);chr=getchar())n=n*10+chr-'0';n*=sign;}
int x[maxn],y[maxn],n;
map<pair<int,int>,int> ma;
pair<int,int> pa;
int main()
{
    freopen("a.in","r",stdin);
    freopen("b.out","w",stdout);
    ri i;
    Read(n);
    ll ans = 0;
    repne(0,n,i){
        Read(x[i]),Read(y[i]);
        pa = make_pair(x[i],y[i]);
        ma[pa]++;
    }
    map<pair<int,int>,int>::iterator it = ma.begin();
    sort(x,x+n),sort(y,y+n);
    int c = 1;
    repne(1,n,i){
        if(x[i]==x[i-1])++c;
        else ans += ((ll)c*(c-1))/2,c = 1;
    }
    ans += ((ll)c*(c-1))>>1;
    c = 1;
    repne(1,n,i){
        if(y[i]==y[i-1])++c;
        else ans += ((ll)c*(c-1))/2,c = 1;
    }
    ans += (ll)c*(c-1)>>1;
    for(;it!=ma.end();++it){
        c = it->second;
        ans = ans - ((ll)c*(c-1))/2;
    }
    cout << ans << endl;
    return 0;
}