PAT (Advanced Level) 1111. Online Map (30)

Posted 2020-08-03 Fighting Heart

预处理出最短路再进行暴力dfs求答案会比较好。直接dfs效率太低。

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

int n,m;
int st,en;
struct Edge
{
    int u,v,len,time;
}e[2000000+10];
int tot=0;
vector<int>g[600];
int Dis[600],Tim[600];
bool flag[600];

int ans_len,ans_time,ans_sz,ans_count;
int path[600],ans_path[600];

vector<int>p1,p2;
int Distance,Time;

void addedge(int u,int v,int len,int time)
{
    e[tot].u=u; e[tot].v=v; e[tot].len=len; e[tot].time=time;
    g[u].push_back(tot++);
}

void SPFA(int s)
{
    queue<int>Q;
    memset(flag,0,sizeof flag);
    for(int i=0;i<=n;i++) Dis[i]=99999999;
    Q.push(s); flag[s]=1; Dis[s]=0;
    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[head]+e[id].len<Dis[e[id].v])
            {
                Dis[e[id].v]=Dis[head]+e[id].len;
                if(flag[e[id].v]==0)
                {
                    flag[e[id].v]=1;
                    Q.push(e[id].v);
                }
            }
        }
    }

    memset(flag,0,sizeof flag);
    for(int i=0;i<=n;i++) Tim[i]=99999999;
    Q.push(s); flag[s]=1; Tim[s]=0;
    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(Tim[head]+e[id].time<Tim[e[id].v])
            {
                Tim[e[id].v]=Tim[head]+e[id].time;
                if(flag[e[id].v]==0)
                {
                    flag[e[id].v]=1;
                    Q.push(e[id].v);
                }
            }
        }
    }
}

void dfs1(int x,int len,int time,int dep)
{
    if(len>ans_len) return;

    if(x==en)
    {
        if(len<ans_len)
        {
            ans_len=len;
            ans_time=time;
            ans_sz=dep;
            for(int i=0;i<dep;i++)
                ans_path[i]=path[i];
        }
        else if(len==ans_len)
        {
            if(time<ans_time)
            {
                ans_time=time;
                ans_sz=dep;
                for(int i=0;i<dep;i++)
                    ans_path[i]=path[i];
            }
        }
        return;
    }
    for(int i=0;i<g[x].size();i++)
    {
        int id=g[x][i];
        path[dep]=e[id].v;
        if(Dis[x]+e[id].len>Dis[e[id].v]) continue;
        dfs1(e[id].v,len+e[id].len,time+e[id].time,dep+1);
    }
}

void dfs2(int x,int time,int count,int dep)
{
    if(time>ans_time) return;

    if(x==en)
    {
        if(time<ans_time)
        {
            ans_time=time;
            ans_count=count;
            ans_sz=dep;
            for(int i=0;i<dep;i++)
                ans_path[i]=path[i];
        }
        else if(time==ans_time)
        {
            if(count<ans_count)
            {
                ans_count=count;
                ans_sz=dep;
                for(int i=0;i<dep;i++)
                    ans_path[i]=path[i];
            }
        }
        return;
    }
    for(int i=0;i<g[x].size();i++)
    {
        int id=g[x][i];
        path[dep]=e[id].v;
        if(Tim[x]+e[id].time>Tim[e[id].v]) continue;
        dfs2(e[id].v,time+e[id].time,count+1,dep+1);
    }
}

int main()
{
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)
    {
        int u,v,f,len,time;
        scanf("%d%d%d%d%d",&u,&v,&f,&len,&time);
        addedge(u,v,len,time);
        if(f==0) addedge(v,u,len,time);
    }
    scanf("%d%d",&st,&en);

    SPFA(st);

    for(int i=0;i<=n;i++) flag[i]=9999999;
    ans_len=9999999;
    ans_time=9999999; flag[st]=0;
    dfs1(st,0,0,0);

    Distance = ans_len;
    p1.push_back(st);
    for(int i=0;i<ans_sz;i++) p1.push_back(ans_path[i]);

    for(int i=0;i<=n;i++) flag[i]=9999999;
    ans_time=9999999;
    ans_count=9999999; flag[st]=0;
    dfs2(st,0,0,0);

    Time=ans_time;
    p2.push_back(st);
    for(int i=0;i<ans_sz;i++) p2.push_back(ans_path[i]);

    bool fail=0;
    if(p1.size()!=p2.size()) fail=1;
    else {
        for(int i=0;i<p1.size();i++)
            if(p1[i]!=p2[i]) fail=1;
    }

    if(fail==0)
    {
        printf("Distance = %d; Time = %d: ",Distance,Time);
        for(int i=0;i<p1.size();i++)
        {
            printf("%d",p1[i]);
            if(i<p1.size()-1) printf(" -> ");
            else printf("\n");
        }
    }
    else
    {
        printf("Distance = %d: ",Distance);
        for(int i=0;i<p1.size();i++)
        {
            printf("%d",p1[i]);
            if(i<p1.size()-1) printf(" -> ");
            else printf("\n");
        }

        printf("Time = %d: ",Time);
        for(int i=0;i<p2.size();i++)
        {
            printf("%d",p2[i]);
            if(i<p2.size()-1) printf(" -> ");
            else printf("\n");
        }

    }
    return 0;
}