寒假训练补题-第十天--I9

原题链接：http://poj.org/problem?id=1287
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.

您被分配设计广泛区域中某些点之间的网络连接。您将获得该区域中的一组点，以及可连接成对点的电缆的一组可能路线。对于两点之间的每条可能路线，您将获得连接该路线上的点所需的电缆长度。请注意，两个给定点之间可能存在许多可能的路径。假设给定的可能路线（直接或间接）连接该区域中的每两个点。您的任务是为该区域设计网络，以便在每两个点之间存在连接（直接或间接）（即，所有点都是互连的，但不一定是通过直接电缆），并且总长度为用过的电缆很小。

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.

输入
输入文件由许多数据集组成。每个数据集定义一个必需的网络。集合的第一行包含两个整数：第一行定义给定点的数量P，第二行定义点之间给定路径的数量R.以下R行定义了点之间的给定路线，每条线给出三个整数：前两个数字标识点，第三个给出路线的长度。数字用空格分隔。仅给出一个数字P = 0的数据集表示输入的结束。数据集用空行分隔。最大点数为50.给定路线的最大长度为100.可能的路线数量不受限制。节点用1和P（含）之间的整数标识。两个点i和j之间的路线可以给出为i j或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.
产量
对于每个数据集，在单独的行上打印一个数字，该行显示用于整个设计网络的电缆的总长度。

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

个人思路：完全没接触过最小生成树，这道题是例子题
ac代码：

#include
#include
#include
#include
#include
using namespace std;
#define CLR(a,b) memset(a,b,sizeof(a))
struct node
{
	int from, to, va;
}a[100010];
int f[100010];
bool cmp(node x, node y)
{
	return x.va < y.va;
}
int find(int x)
{
	if (x != f[x])
		f[x] = find(f[x]);
	return f[x];
}
bool join(int x, int y)
{
	int fx = find(x);
	int fy = find(y);
	if (fx != fy)
	{
		f[fx] = fy;
		return true;
	}
	return false;
}
int main()
{
	int n, m;
	while (~scanf("%d", &n) && n)
	{
		scanf("%d", &m);
		for (int i = 1; i <= n; i++)
			f[i] = i;
		for (int i = 1; i <= m; i++)
			scanf("%d %d %d", &a[i].from, &a[i].to, &a[i].va);
		sort(a + 1, a + 1 + m, cmp);
		int ant = 0;
		int num = 0;
		for (int i = 1; i <= m; i++)
		{
			if (join(a[i].from, a[i].to))
			{
				ant += a[i].va;
				num++;
			}
			if (num == n - 1)		
				break;
		}
		printf("%d\n", ant);
	}
	return 0;
}