VIJOS-P1635 城市连接

Posted 2020-09-16 Winniechen

嘿嘿嘿，逆向spfa，貌似不难...

#include <cstdio>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <iostream>
#include <queue>
using namespace std;
#define N 1005
int n;
int map[N][N];
struct node
{
    int next,to,val;
    int next1,from;
}e[N*N];
int head[N],tail[N],cnt,vis[N],dis[N],a[N];
void add(int x,int y,int z)
{
    e[++cnt].next=head[x];
    e[cnt].to=y;
    e[cnt].val=z;
    head[x]=cnt;
    e[cnt].next1=tail[y];
    e[cnt].from=x;
    tail[y]=cnt;
    return ;
}
int dijkstra(int start)
{
    memset(dis,0x3f,sizeof(dis));
    memset(vis,0,sizeof(vis));
    dis[start]=0;
    for(int i=1;i<=n;i++)
    {
        int x;
        int min_value=0x3f3f3f;
        for(int j=1;j<=n;j++)
        {
            if(vis[j]!=1&&dis[j]<min_value)
            {
                min_value=dis[j];
                x=j;
            }
        }
        vis[x]=1;
        for(int k=head[x];k!=-1;k=e[k].next)
        {
            int ans=e[k].to;
            if(vis[ans]!=1)
            {
                if(dis[ans]>dis[x]+e[k].val)
                {
                    dis[ans]=dis[x]+e[k].val;
                }
            }
        }
    }
    return dis[n];
}
void spfa(int start)
{
    memset(vis,0,sizeof(vis));
    queue <int>q;
    q.push(start);
    vis[start]=1;
    int num=1;
    a[num]=n;
    while(!q.empty())
    {
        int x=q.front();
        q.pop();
        vis[x]=0;
        for(int i=tail[x];i!=-1;i=e[i].next1)
        {
            if(dis[e[i].from]==dis[x]-e[i].val)
            {
                a[++num]=e[i].from;
                q.push(e[i].from);
            }
        }
    }
    return ;
}
int main()
{
    scanf("%d",&n);
    memset(head,-1,sizeof(head));
    memset(tail,-1,sizeof(tail));
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=n;j++)
        {
            scanf("%d",&map[i][j]);
            if(map[i][j]!=0)
            {
                add(i,j,map[i][j]);
            }
        }
    }
    int ans=dijkstra(1);
    spfa(n);
    int i;
    for(i=1;;i++)
    {
        if(a[i+1]==0)break;
    }
    for(;i>=1;i--)
    {
        printf("%d ",a[i]);
    }
    puts("");
    printf("%d\n",ans);
}