POJ 3268 Silver Cow Party

水水更健康。

建立正、反向图。

CODE：

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib> 
#include <queue>
using namespace std;

const int INF = 0x3f3f3f3f;
const int MAXN = 1010;
const int MAXM = 100010;

struct Edge
{
    int v, next, w;
}edge[MAXM];

int n, m, src;
int cnt;

int first[MAXN], d[MAXN], ans[MAXN];
int su[MAXM], sv[MAXM], sw[MAXM];
int MaxTime;

inline void read_graph(int u, int v, int w)
{
    edge[cnt].v = v;
    edge[cnt].w = w;
    edge[cnt].next = first[u], first[u] = cnt++;
}

inline void init()
{
    cnt = 0;
    MaxTime = 0;
    memset(first, -1, sizeof(first));
}

void spfa(int src)
{
    queue<int> q;
    bool inq[MAXN] = {0};
    for(int i = 1; i <= n; i++) d[i] = (i == src)? 0:INF;
    q.push(src);
    while(!q.empty())
    {
        int x = q.front(); q.pop();
        inq[x] = 0;
        for(int e = first[x]; e != -1; e = edge[e].next)
        {
            int v = edge[e].v, w = edge[e].w;
            if(d[v] > d[x] + w)
            {
                d[v] = d[x] + w;
                if(!inq[v])
                {
                    inq[v] = 1;
                    q.push(v);
                }
            }
        }
    }
}

void solve()
{
    init();
    for(int i = 0; i < m; i++)
    {
        scanf("%d%d%d", &su[i], &sv[i], &sw[i]);
        read_graph(su[i], sv[i], sw[i]);
    }
    spfa(src);
    for(int i = 1; i <= n; i++) ans[i] += d[i];
    init();
    for(int i = 0; i < m; i++) read_graph(sv[i], su[i], sw[i]);
    spfa(src);
    for(int i = 1; i <= n; i++)
    {
        ans[i] += d[i];
        MaxTime = max(MaxTime, ans[i]);
    }
    printf("%d\n", MaxTime);
}

int main()
{
    while(~scanf("%d%d%d", &n, &m, &src))
    {
        solve();
    }
    return 0;
}