BZOJ 2100 Apple Delivery

Posted 2020-07-11 ziliuziliu

SPFA双端队列优化。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<deque>
#define maxv 100050
#define maxe 400050
#define inf 0x7f7f7f7f
using namespace std;
struct edge
{
    int v,w,nxt;
}e[maxe];
int n,m,s,t1,t2,nume=0,g[maxv],dis[maxv],a,b,c,ans=inf;
bool vis[maxv];
deque <int> q;
void addedge(int u,int v,int w)
{
    e[++nume].v=v;
    e[nume].w=w;
    e[nume].nxt=g[u];
    g[u]=nume;
}
void spfa(int x)
{
    while (!q.empty())    q.pop_front();
    memset(vis,false,sizeof(vis));
    fill(dis+1,dis+n+1,inf);
    q.push_front(x);vis[x]=true;dis[x]=0;
    while (!q.empty())
    {
        int head=q.front();q.pop_front();vis[head]=false;
        for (int i=g[head];i;i=e[i].nxt)
        {
            int v=e[i].v;
            if (dis[v]>dis[head]+e[i].w)
            {
                dis[v]=dis[head]+e[i].w;
                if (!vis[v])
                {
                    if (q.empty()) q.push_front(v);
                    else if (dis[v]<dis[q.front()]) q.push_front(v);
                    else q.push_back(v);
                }
            }
        }
    }
}
int main()
{
    scanf("%d%d%d%d%d",&m,&n,&s,&t1,&t2);
    for (int i=1;i<=m;i++)
    {
        scanf("%d%d%d",&a,&b,&c);
        addedge(a,b,c);
        addedge(b,a,c);
    }
    spfa(t1);
    ans=dis[s]+dis[t2];
    spfa(t2);
    ans=min(ans,dis[s]+dis[t1]);
    printf("%d\n",ans);
    return 0;
}