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POJ 2421 Constructing Roads

2024-07-19 08:11:09   224人阅读

来源:http://poj.org/problem?id=2421


Constructing Roads
Time Limit: 2000MS Memory Limit: 65536K
Total Submissions: 19645 Accepted: 8193

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

Source

PKU Monthly,kicc

题意: 略。

题解: 图论、最小生成树、Prim。 这题和POJ 1258 基本上是没区别，只是在初始阶段就给它加上了几条边，这些边只要将他们的权值赋值为零就可以了~~


AC代码:

#include<iostream>
#include<cstring>
const int INF=0x3fffffff; 
using namespace std;
int map[105][105],t,n,x,y,wage=0,pb;
bool p[105];
void Prim(){
	int tempx,tempy;
	while(pb--){
		int min=INF;
	for(int i=1;i<=n;i++)
	if(p[i]){
		for(int j=1;j<=n;j++){
			if(!p[j]&&map[i][j]<min){
				tempx=i;tempy=j;
				min=map[i][j];
			}
		}
	}
	p[tempy]=true;
	wage+=min;	
	}
}
int main(){
	memset(p,0,sizeof(p));
	p[1]=true;
	cin>>n;
	pb=n-1;
	for(int i=1;i<=n;i++)
	for(int j=1;j<=n;j++)
	cin>>map[i][j];
	cin>>t;
	while(t--){
		cin>>x>>y;
		map[x][y]=0;
		map[y][x]=0;
	}
	Prim();
	cout<<wage<<endl;
	return 0;
}



POJ 2421 Constructing Roads


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