CodeForces 97B Superset

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A set of points on a plane is called good, if for any two points at least one of the three conditions is true:

those two points lie on same horizontal line;
those two points lie on same vertical line;
the rectangle, with corners in these two points, contains inside or on its borders at least one point of the set, other than these two. We mean here a rectangle with sides parallel to coordinates' axes, the so-called bounding box of the two points.

You are given a set consisting of n points on a plane. Find any good superset of the given set whose size would not exceed 2·105points.

Input

The first line contains an integer n (1 ≤ n ≤ 104) — the number of points in the initial set. Next n lines describe the set's points. Each line contains two integers xi and yi ( - 109 ≤ xi, yi ≤ 109) — a corresponding point's coordinates. It is guaranteed that all the points are different.

Output

Print on the first line the number of points m (n ≤ m ≤ 2·105) in a good superset, print on next m lines the points. The absolute value of the points' coordinates should not exceed 109. Note that you should not minimize m, it is enough to find any good superset of the given set, whose size does not exceed 2·105.

All points in the superset should have integer coordinates.

Sample test(s)
input
21 12 2
output
31 12 21 2

满足三个条件之一就可以了，也不必是最小的集合。即任意两点在同一水平或垂直线上，或者在一个长方形框架上，但是还有其他的点在这个框架的内部或者边缘上，但是由于限制了点最多不能超过2*100000，所以不能强行填满。

#include<stdio.h>#include<iostream>#include<algorithm>#include<set>#define X first#define Y secondusing namespace std;typedef pair<int,int>ii;//pair <int,int>是一个键值对// 键是int类型，值是int类型set<ii>s;//然后这种类型的变量组成一个set，也就是集合//这个集合的变量叫sii a[10020];int n;void F(int l,int r){if(l+1==r)return;int m=l+r>>1;for(int i=l;i<r;i++)s.insert(ii(a[m].X,a[i].Y));F(l,m),F(m,r);}int main(){scanf("%d",&n);for(int i=0;i<n;i++)scanf("%d %d",&a[i].X,&a[i].Y),s.insert(a[i]);sort(a,a+n);F(0,n);printf("%d\n",s.size());for(set<ii>::iterator i=s.begin();i!=s.end();i++)printf("%d %d\n",i->X,i->Y);return 0;}

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