poj 3268 最短路

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<queue>
#include<algorithm>

using namespace std;
#define N 1010
#define INF 0x3f3f3f3f

int maps[N][N];
int n, m, x;
int dist1[N], dist2[N], vis[N];

void Init()
{
    for(int i=1; i<=n; i++)
    for(int j=1; j<=n; j++)
    maps[i][j]=i==j ? 0 : INF;
}

void dij()
{
    for(int i=1; i<=n; i++)
        dist1[i]=maps[i][x];

    memset(vis, 0, sizeof(vis));
    vis[x]=1;
    for(int i=1; i<=n; i++)
    {
        int Min=INF, index=-1;
        for(int j=1; j<=n; j++)
        {
            if(!vis[j]&&dist1[j]<Min)
            {
                Min=dist1[j];
                index=j;
            }
        }
        if(index==-1) break;
        vis[index]=1;
        for(int j=1; j<=n; j++)
        {
            if(!vis[j]&&dist1[j]>maps[j][index]+dist1[index])
                dist1[j]=maps[j][index]+dist1[index];
        }
    }
    for(int i=1; i<=n; i++)
        dist2[i]=maps[x][i];

    memset(vis, 0, sizeof(vis));
    vis[x]=1;
    for(int i=1; i<=n; i++)
    {
        int Min=INF, index=-1;
        for(int j=1; j<=n; j++)
        {
            if(!vis[j]&&dist2[j]<Min)
            {
                Min=dist2[j];
                index=j;
            }
        }
        if(index==-1) break;
        vis[index]=1;
        for(int j=1; j<=n; j++)
        {
            if(!vis[j]&&dist2[j]>dist2[index]+maps[index][j])
                dist2[j]=dist2[index]+maps[index][j];
        }
    }
}

int main()
{
    while(~scanf("%d%d%d", &n, &m, &x))
    {
        Init();
        int u, v, len;
        for(int i=1; i<=m; i++)
        {
            scanf("%d%d%d", &u, &v, &len);
            maps[u][v]=min(len, maps[u][v]);
        }
        dij();

        int ans=-1;

        for(int i=1; i<=n; i++)
        {
            if(dist1[i]+dist2[i]>ans)
                ans=dist1[i]+dist2[i];
        }
        printf("%d\n", ans);
    }
    return 0;
}