UESTC 914 方老师的分身I Dijkstra

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#define Mod 1000000007
using namespace std;
#define N 1007

int mp[N][N],n,m;
int dis[N],vis[N],dis2[N];

void Dijastra(int s,int *dis)
{
    int now = s;
    int i,k;
    dis[now] = 0;
    vis[now] = 1;
    for(i=1;i<=n;i++)
    {
        for(k=1;k<=n;k++)  //order 1
        {
            if(mp[now][k] != Mod && dis[now] + mp[now][k] < dis[k])
                dis[k] = dis[now] + mp[now][k];
        }
        int mini = Mod;   //order 2
        for(k=1;k<=n;k++)
        {
            if(dis[k] < mini && !vis[k])
            {
                now = k;
                mini = dis[k];
            }
        }
        vis[now] = 1;
    }
}

int main()
{
    int u,v,w,i,j,x;
    while(scanf("%d%d%d",&n,&m,&x)!=EOF)
    {
        for(i=1;i<=n;i++)
            dis[i] = Mod;
        dis[x] = 0;
        for(i=1;i<=n;i++)
        {
            for(j=i;j<=n;j++)
                mp[i][j] = mp[j][i] = Mod;
            mp[i][i] = 0;
        }
        while(m--)
        {
            scanf("%d%d%d",&u,&v,&w);
            mp[u][v] = w;
        }
        memset(vis,0,sizeof(vis));
        Dijastra(x,dis);
        for(i=1;i<=n;i++)
            dis2[i] = Mod;
        dis2[x] = 0;
        for(i=1;i<=n;i++)
        {
            for(j=i+1;j<=n;j++)
            {
                swap(mp[i][j],mp[j][i]);
            }
        }
        memset(vis,0,sizeof(vis));
        Dijastra(x,dis2);
        int maxi = -1;
        for(i=1;i<=n;i++)
        {
            if(dis[i] < Mod && dis2[i] < Mod)
                maxi = max(maxi,dis[i]+dis2[i]);
        }
        printf("%d\n",maxi);
    }
    return 0;
}