CF 217A A. Ice Skating（贪心）

Bajtek is learning to skate on ice. He's a beginner, so his only mode of transportation is pushing off from a snow drift to the north, east, south or west and sliding until he lands in another snow drift. He has noticed that in this way it's impossible to get from some snow drifts to some other by any sequence of moves. He now wants to heap up some additional snow drifts, so that he can get from any snow drift to any other one. He asked you to find the minimal number of snow drifts that need to be created.

We assume that Bajtek can only heap up snow drifts at integer coordinates.

Input

The first line of input contains a single integer n (1 ≤ n ≤ 100) — the number of snow drifts. Each of the following n lines contains two integers xi and yi (1 ≤ xi, yi ≤ 1000) — the coordinates of the i-th snow drift.

Note that the north direction coinсides with the direction of Oy axis, so the east direction coinсides with the direction of the Ox axis. All snow drift's locations are distinct.

Output

Output the minimal number of snow drifts that need to be created in order for Bajtek to be able to reach any snow drift from any other one.

Sample test(s)

input

2
2 1
1 2

output

1

input

2
2 1
4 1

output

0

http://codeforces.com/contest/217/problem/A

在一个整数坐标系中，一直有很多整数点集。就像冰上滑雪一样只能够东南西北移动，在坐标系中即横竖移动。为了保证任意一点到任意一点都能到达，需要建立一些点能够做到，问题就是求出最少点的数量。

#include<iostream>
#include<algorithm>
#include<string>    
using namespace std;
int x[101],y[101],z[101];
int n,s=0;
void dfs(int i){
    z[i]=1;
    for(int j=0;j<n;++j){
        if(z[j]!=1&&(x[i]==x[j]||y[i]==y[j]))
            dfs(j);}}
int main(){
    cin>>n;
    for(int i=0;i<n;++i)
        cin>>x[i]>>y[i];
    for(int i=0;i<n;++i){
        if(z[i]!=1){
            dfs(i);
            s++;}}
    cout<<s-1;
    return 0;
}