hdu 4738 Caocao's Bridges(割边)

墨蓝 2021-12-03 06:19 188阅读 0赞

[题目链接][Link 1]

用tarjan求桥上的最小权值

#include<bits/stdc++.h>
    #define ll long long int
    using namespace std;
    inline ll gcd(ll a,ll b){
         return b?gcd(b,a%b):a;}
    inline ll lcm(ll a,ll b){
         return a/gcd(a,b)*b;}
    int moth[13]={
        0,31,28,31,30,31,30,31,31,30,31,30,31};
    int dir[4][2]={
        1,0 ,0,1 ,-1,0 ,0,-1};
    int dirs[8][2]={
        1,0 ,0,1 ,-1,0 ,0,-1, -1,-1 ,-1,1 ,1,-1 ,1,1};
    const int inf=0x3f3f3f3f;
    const int N=1e6+7;
    const ll mod=1e9+7;
    struct edge{
        int v,next,w;
    };
    edge e[N<<1];
    int head[N],cnt = 1,dfn[N],low[N],num = 0,bridge[N];
    void init(){
        memset(head,0,sizeof(head));
        memset(dfn,0,sizeof(dfn));
        memset(low,0,sizeof(low));
        memset(bridge,0,sizeof(bridge));
        cnt=1; num=0;
    }
    void add(int u,int v,int w){
        e[++cnt].next=head[u]; e[cnt].v=v; e[cnt].w=w;
        head[u]=cnt;
    }
    void tarjan(int u,int edge){
        dfn[u]=low[u]=++num;
        for(int i=head[u];i;i=e[i].next){
            int v=e[i].v; int w=e[i].w;
            if(!dfn[v]){
                tarjan(v,i);
                low[u]=min(low[u],low[v]);
                if(low[v]>dfn[u])
                    bridge[i]=bridge[i^1]=1;
            }else if(i!=(edge^1))
                low[u]=min(low[u],low[v]);
        }
    }
    int main(){
        ios::sync_with_stdio(false);
        cin.tie(0);
        int n,m; 
        while(cin>>n>>m){
            if(n==0&&m==0) break;
            init();
            for(int i=1;i<=m;i++){
                int u,v,w; cin>>u>>v>>w;
                add(u,v,w); add(v,u,w);
            }
            tarjan(1,-1);
            bool f=0;
            for(int i=1;i<=n;i++)
                if(!dfn[i]) f=1;
            if(f){
                cout<<"0\n";
                continue;
            }
            int ans=inf;
            for(int i=2;i<=cnt;i++){
                if(bridge[i])
                    ans=min(ans,e[i].w);
            }
            if(ans==inf) cout<<"-1\n";
            else{
                if(ans==0) cout<<"1\n";
                else cout<<ans<<"\n";
            } 
        }
        return 0;
    }

转载于:https://www.cnblogs.com/wmj6/p/11153797.html

[Link 1]: http://acm.hdu.edu.cn/showproblem.php?pid=4738