find the mincost route【无向图最小环】

 1 #include<stdio.h>
 2 #include<algorithm>
 3 #define LL long long
 4 #define mem(a, b) memset(a, b, sizeof(a))
 5 using namespace std;
 6 const LL inf = 0x3f3f3f3f;
 7 const int MAXN = 110;
 8 
 9 int n, m;
10 LL dis[MAXN][MAXN], map[MAXN][MAXN];//最短路径 直接路径 
11 LL ans;
12 
13 void floyd()
14 {
15     ans = inf;
16     for(int k = 1; k <= n; k ++) //枚举中点 
17     {
18         for(int i = 1; i < k; i ++) //起点 
19             for(int j = i + 1; j < k; j ++)//终点 
20                 ans = min(ans, map[i][k] + map[k][j] + dis[i][j]); //在dis没更新倒k之前，是没有经过k点的。所以保证了至少3个不同的点 
21         for(int i = 1; i <= n; i ++)
22             for(int j = 1; j <= n; j ++)
23                 dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]);
24     }
25     if(ans != inf)
26         printf("%lld\n", ans);
27     else
28         printf("It‘s impossible.\n");
29 }
30 
31 int main()
32 {
33     while(scanf("%d%d", &n, &m) != EOF)
34     {
35         for(int i = 1; i <= n; i ++)
36             for(int j = 1; j <= n; j ++)
37             {
38                 if(i == j)
39                     dis[i][j] = map[i][j] = 0;
40                 else
41                     dis[i][j] = map[i][j] = inf;
42             }
43         for(int i = 1; i <= m; i ++)
44         {
45             int a, b;
46             LL c;
47             scanf("%d%d%lld", &a, &b, &c);
48             dis[a][b] = dis[b][a] = map[a][b] = map[b][a] = min(map[a][b], c);//双向边 
49         }
50         floyd();
51     }
52     return 0;
53 }