就是求最小权值的桥。。不过有好几个坑。。。
1：原图不连通，ans=0.
2： m<=n^2 显然有重边，重边必然不是桥，处理重边直接add(u, v, INF).
3: 最小桥边权为0的时候，ans=1，至少要派一个人运炸弹。。。
#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<queue>
#include<stack>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<fstream>
#include<sstream>
#include<map>
#include<set>
using namespace std; const int N = 1111;
const int INF = 100000000;
int n, m;
int pre[N], low[N], dfs_clock;
int bccno[N], vis[N], wi[N][N], g[N][N];
struct Edge
{
//flag = 1 ->bridge
int from, to, w, flag;
};
vector<int> G[N];
vector<Edge> edges; //add bidir edge
void addedge(int u, int v, int w)
{
edges.push_back((Edge){u, v, w, 0});
edges.push_back((Edge){v, u, w, 0});
int nima = edges.size();
G[u].push_back(nima-2);
G[v].push_back(nima-1);
} int dfs(int u, int fa)
{
int lowu = pre[u] = ++dfs_clock;
int sz = G[u].size();
for(int i=0; i<sz; i++)
{
int v = edges[G[u][i]].to;
if(!pre[v])
{
int lowv = dfs(v, u);
lowu = min(lowu, lowv);
if(lowv > pre[u]) edges[G[u][i]].flag = 1, edges[G[u][i]^1].flag = 1;
}
else if(pre[v] < pre[u] && v != fa) lowu = min(lowu, pre[v]);
}
return low[u] = lowu;
} void dfs1(int u)
{
vis[u] = 1;
int sz = G[u].size();
for(int i=0; i<sz; i++)
{
Edge e = edges[G[u][i]];
int v = e.to;
if(!vis[v]) dfs1(v);
}
}
int u, v, w; int main()
{
while(scanf("%d%d", &n, &m), n+m)
{
for(int i=0; i<n+1; i++) G[i].clear();
edges.clear();
memset(g, 0, sizeof(g));
for(int i=0; i<m; i++)
{
scanf("%d%d%d", &u, &v, &w); u--; v--;
g[u][v]++; //BIANSHU
g[v][u]++;
wi[u][v] = w;
} //CHONG BIAN
for(int i=0; i<n; i++)
for(int j=0; j<n; j++)
{
if(g[i][j] == 1) addedge(i, j, wi[i][j]);
else if(g[i][j] > 1) addedge(i, j, INF);
} //BU LIANTONG
memset(vis, 0, sizeof(vis));
dfs1(0);
bool flag = 0;
for(int i=0; i<n; i++)
{
if(!vis[i])
{
flag = 1;
break;
}
}
if(flag)
{
puts("0");
continue;
}
//QIAO
memset(pre, 0, sizeof(pre));
dfs_clock = 0;
for(int i=0; i<n; i++) if(!pre[i]) dfs(i, -1);
int ans = INF;
int sz = edges.size();
for(int i=0; i<sz; i++) if(edges[i].flag == 1) ans = min(ans, edges[i].w);
if(ans == INF) puts("-1");
else printf("%d\n", ans == 0 ? 1 : ans); //0 -> 1
}
return 0;
}