AYIT2017暑假集训第二周周三赛 C - Highways POJ - 1751

The island nation of Flatopia is perfectly flat. Unfortunately, Flatopia has a very poor system of public highways. The Flatopian government is aware of this problem and has already constructed a number of highways connecting some of the most important towns. However, there are still some towns that you can't reach via a highway. It is necessary to build more highways so that it will be possible to drive between any pair of towns without leaving the highway system. 

Flatopian towns are numbered from 1 to N and town i has a position given by the Cartesian coordinates (xi, yi). Each highway connects exaclty two towns. All highways (both the original ones and the ones that are to be built) follow straight lines, and thus their length is equal to Cartesian distance between towns. All highways can be used in both directions. Highways can freely cross each other, but a driver can only switch between highways at a town that is located at the end of both highways. 

The Flatopian government wants to minimize the cost of building new highways. However, they want to guarantee that every town is highway-reachable from every other town. Since Flatopia is so flat, the cost of a highway is always proportional to its length. Thus, the least expensive highway system will be the one that minimizes the total highways length. 

Input

The input consists of two parts. The first part describes all towns in the country, and the second part describes all of the highways that have already been built. 

The first line of the input file contains a single integer N (1 <= N <= 750), representing the number of towns. The next N lines each contain two integers, xi and yi separated by a space. These values give the coordinates of i ^th town (for i from 1 to N). Coordinates will have an absolute value no greater than 10000. Every town has a unique location. 

The next line contains a single integer M (0 <= M <= 1000), representing the number of existing highways. The next M lines each contain a pair of integers separated by a space. These two integers give a pair of town numbers which are already connected by a highway. Each pair of towns is connected by at most one highway. 

Output

Write to the output a single line for each new highway that should be built in order to connect all towns with minimal possible total length of new highways. Each highway should be presented by printing town numbers that this highway connects, separated by a space. 

If no new highways need to be built (all towns are already connected), then the output file should be created but it should be empty. 

Sample Input

9
1 5
0 0 
3 2
4 5
5 1
0 4
5 2
1 2
5 3
3
1 3
9 7
1 2

Sample Output

1 6
3 7
4 9
5 7
8 3

很无语的一道题，题目说的是给你几个点并且把点坐标给你，然后又给你说哪几条路建好了，然后让你输出剩下还需要建的，就是最小生成树问题。

这道题不知道为什么在输入已经建好的路的时候用while会出错，虽然答案一样，但是用while会超时，for就不会

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
#include<algorithm>
using namespace std;
struct note//存储点坐标和点与点之间的长度
{
    int x,y;
    double w;
} l[2000000];
struct st//存储点坐标
{
    int u,v;
} l1[2000000];
int f[2000];//存储根节点
double cmp(note a,note b)//比较函数，因为算的是距离，所以用浮点型
{
    return a.w<b.w;
}
int gf(int v)//找根的递归函数
{
    if(f[v]==v)
        return v;
    else
    {
        f[v]=gf(f[v]);
        return f[v];
    }
}

int mer(int v,int u)//对树进行合并
{
    int t1,t2;
    t1=gf(v);
    t2=gf(u);
    if(t1!=t2)
    {
        f[t2]=t1;
        return 1;
    }
    return 0;
}
int main()
{
    int a,b,j,n,m,i;
    while(~scanf("%d",&n))//输入有几个点
    {
        for(i=1; i<=n; i++)//输入点坐标
        {
            scanf("%d%d",&l1[i].u,&l1[i].v);
            f[i]=i;//初始化各个顶点的根
        }
        int ca=0;
        for(i=1; i<=n; i++)//计算两点之间距离并进行存储
        {
            for(j=i+1; j<=n; j++)
            {
                l[ca].x=i;
                l[ca].y=j;
                l[ca++].w=(l1[i].u-l1[j].u)*(l1[i].u-l1[j].u)+(l1[i].v-l1[j].v)*(l1[i].v-l1[j].v);
                l[ca].x=j;
                l[ca].y=i;
                l[ca++].w=(l1[i].u-l1[j].u)*(l1[i].u-l1[j].u)+(l1[i].v-l1[j].v)*(l1[i].v-l1[j].v);
            }
        }
        scanf("%d",&m);
        for(i=1;i<=m;i++)
        {
            scanf("%d%d",&a,&b);//输入已经建好的路，并对其进行
            mer(a,b);
        }
        sort(l,l+ca,cmp);
        int count1=0;
        for(i=0;i<ca;i++)
        {
            if(mer(l[i].x,l[i].y))
            {
                printf("%d %d\n",l[i].x,l[i].y);
                count1++;
            }
            if(count1==n-1)break;
        }
        //if(count1==0)
          //  printf("\n");
    }
    return 0;
}