PAT (Advanced Level) 1018. Public Bike Management (30)

#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cstdio>
#include<queue>
#include<vector>
using namespace std;

const int INF=0x7FFFFFFF;
const int maxn=550;
int n,m,C1,C2,tot;
int Cmax;
int val[maxn];
struct Edge
{
    int u,v,L;
}e[600000];
int f[600000];
vector<int>g[maxn];
int dis[2][maxn];

int ans[maxn],cnt;
int sta[maxn];

int MIN1,MIN2;

void init()
{
    MIN1=MIN2=INF;
    tot=0;C1=0;
    for(int i=0;i<=500;i++) g[i].clear();
}

void add(int a,int b,int c)
{
    e[tot].u=a,e[tot].v=b,e[tot].L=c;
    g[a].push_back(tot);
    tot++;
}

void read()
{
    scanf("%d%d%d%d",&Cmax,&n,&C2,&m);
    for(int i=1;i<=n;i++) scanf("%d",&val[i]);
    for(int i=1;i<=m;i++)
    {
        int u,v,L; scanf("%d%d%d",&u,&v,&L);
        add(u,v,L);
        add(v,u,L);
    }
}

void SPFA(int f,int st)
{
    for(int i=0;i<=500;i++) dis[f][i]=INF;
    dis[f][st]=0;
    int flag[maxn]; memset(flag,0,sizeof flag);
    queue<int>Q; Q.push(st); flag[st]=1;
    while(!Q.empty())
    {
        int head= Q.front(); Q.pop(); flag[head]=0;
        for(int i=0;i<g[head].size();i++)
        {
            int id=g[head][i];
            if(dis[f][head]+e[id].L<dis[f][e[id].v])
            {
                dis[f][e[id].v]=dis[f][head]+e[id].L;
                if(flag[e[id].v]==0)
                {
                    Q.push(e[id].v);
                    flag[e[id].v]=1;
                }
            }
        }
    }
}

void dfs(int x,int num1,int num2,int deep)
{
    sta[deep]=x;

    if(x==C2)
    {
        if(num2<MIN2)
        {
            MIN2=num2;
            MIN1=num1;
            for(int i=0;i<=deep;i++) ans[i]=sta[i];
            tot=deep;
        }

        else if(num2==MIN2&&num1<MIN1)
        {
            MIN2=num2;
            MIN1=num1;
            for(int i=0;i<=deep;i++) ans[i]=sta[i];
            tot=deep;
        }
        return;
    }

    for(int i=0;i<g[x].size();i++)
    {
        if(f[g[x][i]]==0) continue;
        int to=e[g[x][i]].v;

        if(val[to]==Cmax/2) dfs(to,num1,num2,deep+1);
        else if(val[to]>Cmax/2) dfs(to,num1+val[to]-Cmax/2,num2,deep+1);
        else if(val[to]<Cmax/2)
        {
            if(num1>Cmax/2-val[to]) dfs(to,num1+val[to]-Cmax/2,num2,deep+1);
            else dfs(to,0,num2+Cmax/2-val[to]-num1,deep+1);
        }
    }
}

void work()
{
    int len=dis[0][C2];

    for(int i=0;i<tot;i++)
        if(dis[0][e[i].u]+e[i].L+dis[1][e[i].v]==len)
            f[i]=1;

    dfs(0,0,0,0);

    printf("%d ",MIN2);
    for(int i=0;i<=tot;i++)
    {
        if(i<tot) printf("%d->",ans[i]);
        else printf("%d ",ans[i]);
    }
    printf("%d\n",MIN1);
}

int main()
{
    init();
    read();
    SPFA(0,C1);
    SPFA(1,C2);
    work();
    return 0;
}