hdu4738（割桥）

找人去炸边，炸完之后分成两个连通块（炸割桥）

每条边上有w个守卫，派去炸桥的人不能比守卫少

所以，

如果原本不连通，那么输出0

如果没有桥，输出-1

如果有桥没有守卫，那么是输出1，而不是0（trick）

 1 #pragma warning(disable:4996)
 2 #pragma comment(linker, "/STACK:1024000000,1024000000")
 3 #include <iostream>
 4 #include <stdio.h>
 5 #include <string.h>
 6 #include <vector>
 7 #include <stack>
 8 #include <queue>
 9 #include <math.h>
10 #include <algorithm>
11 #include <map>
12 #include <set>
13 #include <functional>
14 using namespace std;
15 const int INF = 1 << 30;
16 typedef __int64 LL;
17 /*
18 要摧毁的边只能是桥
19 
20 */
21 
22 const int N = 1000 + 10;
23 int head[N], next[N*N], to[N*N], dist[N*N], e;
24 int dfn[N], low[N], dfs_clock, ans;
25 void init()
26 {
27     memset(head, -1, sizeof(head));
28     memset(dfn, 0, sizeof(dfn));
29     memset(low, 0, sizeof(low));
30     dfs_clock = e = 0;
31     ans = INF;
32 }
33 void addEdge(int u, int v, int dis)
34 {
35     to[e] = v;
36     dist[e] = dis;
37     ::next[e] = head[u];
38     head[u] = e++;
39 }
40 void tarjan(int u, int fa)
41 {
42     dfn[u] = low[u] = ++dfs_clock;
43     bool flag = false;
44     for (int i = head[u]; i + 1; i = ::next[i])
45     {
46         if (to[i] == fa && !flag)
47         {
48             flag = true;
49             continue;
50         }
51         if(dfn[to[i]]==0)
52             tarjan(to[i], u);
53         low[u] = min(low[to[i]], low[u]);
54         if (low[to[i]] > dfn[u])
55             ans = min(ans, dist[i]);
56     }
57 }
58 int main()
59 {
60     int n, m;
61     while (scanf("%d%d", &n, &m),n+m)
62     {
63         int u, v, dis;
64         init();
65         for (int i = 1;i <= m;++i)
66         {
67             scanf("%d%d%d", &u, &v, &dis);
68             addEdge(u, v, dis);
69             addEdge(v, u, dis);
70         }
71         ans = INF;
72         tarjan(1, -1);
73         bool flag = true;
74         for (int i = 1;i <= n;++i)
75             if (dfn[i] == 0)
76             {
77                 printf("0
");
78                 flag = false;
79                 break;
80             }
81         if (!flag)continue;
82         if (ans == INF)
83             ans = -1;
84         if (ans == 0)ans = 1;
85         printf("%d
", ans);
86     }
87     return 0;
88 }