HDU 1599 find the mincost route 无向图最小环

题目来源：HDU 1599 find the mincost route

题意：求最小的3点组成的环

思路：floyd

http://blog.sina.com.cn/s/blog_476a25110100mag6.html 

http://www.cppblog.com/mythit/archive/2009/04/21/80579.aspx

#include 
#include 
#include 
using namespace std;
const int maxn = 110; 
int a[maxn][maxn];
int d[maxn][maxn];
int n, m, ans;
void floyd()
{
	 for(int k = 1; k <= n; k++)
	 {
	 	for(int i = 1; i < k; i++)
	 	{
	 		for(int j = i+1; j < k; j++)
	 		{
	 			ans = min(ans, d[i][j]+a[i][k]+a[k][j]); 
	 		}
	 	}
	 	for(int i = 1; i <= n; i++)
	 	{
	 		for(int j = 1; j <= n; j++)
	 		{
	 			d[i][j] = min(d[i][j], d[i][k]+d[k][j]); 
	 		}
	 	}
	 }
}
int main()
{
	while(scanf("%d %d", &n, &m) != EOF)
	{
		for(int i = 0; i <= n; i++)
		{
			for(int j = 0; j <= n; j++)
			{
				if(i == j)
					a[i][j] = d[i][j] = 0;
				else
					a[i][j] = d[i][j] = 99999999;
			}
		}
		while(m--)
		{
			int u, v, w;
			scanf("%d %d %d", &u, &v, &w); 
			if(a[u][v] > w)
			{
				a[u][v] = w;
				a[v][u] = w;
				d[u][v] = w;
				d[v][u] = w;
			}
		}
		ans = 99999999;
		floyd(); 
		if(ans == 99999999)
			puts("It's impossible.");
		else
	 		printf("%d\n", ans);
	}
	return 0;
}