1169 networking.cpp

/* Name: soj 1169: Networking From: Computer Science Department of Sichuan University Author:

/*   1169: Networking

You are assigned to design network connections between certain points in a wide area. 
You are given a set of points in the area, and a set of possible routes for the cables 
that may connect pairs of points. For each possible route between two points, you are 
given the length of the cable that is needed to connect the points over that route. Note 
that there may exist many possible routes between two given points. It is assumed that 
the given possible routes connect (directly or indirectly) each two points in the area.

Your task is to design the network for the area, so that there is a connection (direct 
or indirect) between every two points (i.e., all the points are interconnected, but not 
necessarily by a direct cable), and that the total length of the used cable is minimal.


Input

The input file consists of a number of data sets. Each data set defines one required 
network. The first line of the set contains two integers: the first defines the number 
P of the given points, and the second the number R of given routes between the points. 
The following R lines define the given routes between the points, each giving three integer 
numbers: the first two numbers identify the points, and the third gives the length of the 
route. The numbers are separated with white spaces. A data set giving only one number P=0 
denotes the end of the input. The data sets are separated with an empty line.

The maximal number of points is 50. The maximal length of a given route is 100. The number 
of possible routes is unlimited. The nodes are identified with integers between 1 and P 
(inclusive). The routes between two points i and j may be given as i j or as j i.


Output

For each data set, print one number on a separate line that gives the total length of the 
cable used for the entire designed network.


Sample Input

1 0

2 3
1 2 37
2 1 17
1 2 68

3 7
1 2 19
2 3 11
3 1 7
1 3 5
2 3 89
3 1 91
1 2 32

5 7
1 2 5
2 3 7
2 4 8
4 5 11
3 5 10
1 5 6
4 2 12

0


Sample Output

0
17
16
26
*/


/*
  Name: soj 1169: Networking
  From: Computer Science Department of Sichuan University 
  Author: LoyaltyJi
  Date: 03-05-06 00:35
  Description:   求最小生成树经典题!
*/

#include <stdio.h>
#include <limits.h>

#define MaxN 50 + 5

int P, V;
int Edge[MaxN][MaxN];

void Prim() {
	int i, j;
	int *lowcost = new int[P];
	int *nearvex = new int[P];

	for(i = 2; i <= P; i ++) {
		lowcost[i] = Edge[1][i];
		nearvex[i] = 0;
	}
	nearvex[1] = -1, lowcost[1] = 0;

	for(i = 2; i <= P; i ++) {
		int min = INT_MAX;
		int v = 0; 

		for(j = 1; j <= P; j ++) {
			if(nearvex[j] != -1 && lowcost[j] < min)
				v = j, min = lowcost[j];
		}

		if( v ) {
			nearvex[v] = -1;
			for(j = 2; j <= P; j ++) {
				if(nearvex[j] != -1 && Edge[v][j] < lowcost[j])
					lowcost[j] = Edge[v][j], nearvex[j] = v;
			}
		}
	}

	int ans = 0;
	for(i = 1; i <= P; i ++) {
		ans += lowcost[i];
//		printf("%d ", lowcost[i]);
	}

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

	return ;
}

bool init() {
	scanf("%d", &P);
	if(P == 0)  return false;

	int i, j, a, b, c;
	scanf("%d", &V);

	for(i = 1; i <= P; i ++) {   // init
		for(j = 1; j <= P; j ++) 
			Edge[i][j] = INT_MAX;
	}
	for(i = 1; i <= P; i ++) Edge[i][i] = 0;

	for(i = 0; i < V; i ++) {
		scanf("%d %d %d", &a, &b, &c);	
		if(c < Edge[a][b])  Edge[a][b] = Edge[b][a] = c;
	}

//	for(i = 1; i <= P; i ++) {
//		for(j = 1; j <= P; j ++)
//			printf("%d ", Edge[i][j]);
//		printf("\n");
//	}

	return true;
}

void solve() {
	Prim();
	return ;
}

int main() {
	while( init() )
		solve();
	return 0;
}