HDU 4738 Caocao's Bridges(Tarjan)

题目链接

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
#include <cstdlib>
using namespace std;
#define N 1001
#define M 20000001
#define INF 0x3f3f3f3f
struct node
{
    int u,v,next;
}edge[M];
int first[N],DFN[N],Belong[N],stack[N],Low[N],cnum[N];
int in[N],d[N];
int qu[M],qv[M],qw[M];
int n,m;
bool vis[M];
int tot,scnt,top;
int o[M];
void CL()
{
    tot = scnt = top = 0;
    memset(first,-1,sizeof(first));
    memset(in,0,sizeof(in));
    memset(DFN,0,sizeof(DFN));
    memset(vis,0,sizeof(vis));
}
void add(int u,int v,int w)
{
    edge[tot].u = u;
    edge[tot].v = v;
    edge[tot].next = first[u];
    first[u] = tot ++;
}
void Tarjan(int u)
{
    int v,i;
    DFN[u] = Low[u] = ++ tot;
    stack[top++] = u;
    in[u] = 1;
    for(i = first[u];i != -1;i = edge[i].next)
    {
        v = edge[i].v;
        if(vis[i]) continue;
        vis[i] = vis[i^1] = 1;
        if(!DFN[v])
        {
            Tarjan(v);
            Low[u] = min(Low[u],Low[v]);
        }
        else
        {
            Low[u] = min(Low[u],DFN[v]);
        }
    }
    if(DFN[u] == Low[u])
    {
        scnt ++;
        do
        {
            v = stack[--top];
            Belong[v] = scnt;
            in[v] = 0;
            cnum[scnt] ++;
        }while(u != v);
    }
}
int find(int x)
{
    int r,t;
    r = x;
    while(o[x] != x)
    x = o[x];
    while(r != x)
    {
        t = o[r];
        o[r] = x;
        r = t;
    }
    return x;
}
void merge(int x,int y)
{
    x = find(x);
    y = find(y);
    if(x != y)
    o[x] = y;
}
int main()
{
    int n,m,i,u,v,w,minz;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        if(n == 0&&m == 0) break;
        CL();
        for(i = 1;i <= n;i ++)
        {
            o[i] = i;
        }
        for(i = 0;i < m;i ++)
        {
            scanf("%d%d%d",&u,&v,&w);
            qu[i] = u;
            qv[i] = v;
            qw[i] = w;
            merge(u,v);
            add(u,v,w);
            add(v,u,w);
        }
        int fa = find(1);
        for(i = 2;i <= n;i ++)
        {
            if(find(i) != fa)
            break;
        }
        if(i != n+1)
        {
            printf("0
");
            continue;
        }
        minz = 10000000;
        Tarjan(1);
        for(i = 0;i < m;i ++)
        {
            if(Belong[qu[i]] != Belong[qv[i]])
            {
                minz = min(minz,qw[i]);
            }
        }
        if(scnt == 1)
        printf("-1
");
        else
        {
            if(minz == 0)
            printf("1
");
            else
            printf("%d
",minz);
        }
    }

}