LUOGU P1186 玛丽卡

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>

using namespace std;
const int MAXN = 1005;
const int MAXM = 1000005;

inline int rd(){
    int x=0,f=1;char ch=getchar();
    while(!isdigit(ch)) {f=ch==‘-‘?0:1;ch=getchar();}
    while(isdigit(ch))  {x=(x<<1)+(x<<3)+ch-‘0‘;ch=getchar();}
    return f?x:-x;
}

int n,m,head[MAXN],cnt=1,fa[MAXN],dis[MAXN],ans;
bool cut[MAXM],vis[MAXN];
int to[MAXM<<1],nxt[MAXM<<1],val[MAXM<<1];

struct Node{
    int w,id;
    friend bool operator<(const Node A,const Node B){
        return A.w>B.w;
    }
};

priority_queue<Node> Q;

inline void add(int bg,int ed,int w){
    to[++cnt]=ed,nxt[cnt]=head[bg],val[cnt]=w,head[bg]=cnt;
}

void dijkstra(bool flag){
    memset(dis,0x3f,sizeof(dis));
    memset(vis,false,sizeof(vis));
    Node now;now.id=1;now.w=0;dis[1]=0;Q.push(now);
    while(!Q.empty()){
        Node zz=Q.top();Q.pop();int x=zz.id;
        if(dis[x]!=zz.w || vis[x]) continue;vis[x]=1;
        for(register int i=head[x];i;i=nxt[i]){
            if(cut[i]) continue;int u=to[i];
            if(dis[u]<=dis[x]+val[i]) continue;
            if(flag) fa[u]=x;
            dis[u]=dis[x]+val[i];
            now.id=u;now.w=dis[u];Q.push(now);
        }
    }    
    if(flag) return;
    ans=max(ans,dis[n]);
}

int main(){
    n=rd(),m=rd();int x,y,z;
    for(register int i=1;i<=m;i++){
        x=rd(),y=rd(),z=rd();
        add(x,y,z),add(y,x,z);
    }
    dijkstra(1);    
    int now=n,k;
    while(fa[now]){
        for(register int i=head[now];i;i=nxt[i])
            if(to[i]==fa[now]) {cut[i]=cut[i^1]=1;k=i;break;}
        dijkstra(0);
        now=fa[now];cut[k]=cut[k^1]=0;
    }
    printf("%d",ans);
    return 0;
}