hust 1102 Constructing Roads

Problem Description

There are N villages, which are numbered from 1 to N,
and you should build some roads such that every two villages can connect to each
other. We say two village A and B are connected, if and only if there is a road
between A and B, or there exists a village C such that there is a road between A
and C, and C and B are connected. 

We know that there are already
some roads between some villages and your job is the build some roads such that
all the villages are connect and the length of all the roads built is
minimum.

Input

The first line is an integer N (3 <= N <= 100),
which is the number of villages. Then come N lines, the i-th of which contains N
integers, and the j-th of these N integers is the distance (the distance should
be an integer within [1, 1000]) between village i and village j.

Then
there is an integer Q (0 <= Q <= N * (N + 1) / 2). Then come Q lines, each
line contains two integers a and b (1 <= a < b <= N), which means the
road between village a and village b has been built.

Output

You should output a line contains an integer, which
is the length of all the roads to be built such that all the villages are
connected, and this value is minimum.

Sample Input

3

0 990 692

990 0 179

692 179 0

1

1 2

Sample Output

179

很简单的最小生成树，只要把已经有了的边的cost设为0就可以了

#include<iostream>

#include<cstdio>

#include<vector>

#include<algorithm>

using namespace std;

const int MAX=1000000;

struct node

{

    int left,right,cost;

}road[MAX];

bool cmp(node x,node y){return x.cost<y.cost;}
int p[MAX],m,n;
int find(int x){return x==p[x]? x:p[x]=find(p[x]);}
int kruskal()

{

    int ans=0;

    for (int i=0;i<=n;i++) p[i]=i;

    for (int i=0;i<m;i++)

    {

        int x=find(road[i].left);

        int y=find(road[i].right);

        if(x!=y)

        {

            ans+=road[i].cost;

            p[x]=y;

        }

    }

    return ans;

}
int main()

{

    int x,y,c,G[101][101],q;

    while(scanf("%d",&n)!=EOF)

    {

        for (int i=1;i<=n;i++)

        for (int j=1;j<=n;j++)

        scanf("%d",&G[i][j]);

        scanf("%d",&q);

        for (int i=0;i<q;i++)

        {

            scanf("%d%d",&x,&y);

            G[x][y]=0;

        }

        m=0;

        for (int i=1;i<=n;i++)

        for (int j=1;j<=n;j++)

        {

            if (i!=j)

            {

                road[m].left=i;

                road[m].right=j;

                road[m].cost=G[i][j];

                m++;

            }

        }

        sort(road,road+m,cmp);

        printf("%d\n",kruskal());

    }

    return 0;

}

hust 1102 Constructing Roads