poj3268

又犯了同样的错误，开edge数组开小了，应该是maxm,开成了maxn

正反两个图，进行两次dijkstra即可

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

#define maxn 1005
#define maxm 100005
#define inf 1000000000

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

int n, m, t, head[maxn], ophead[maxn];
int tot, optot, len[maxn], oplen[maxn];

void init()
{
    tot = 0;
    optot = 0;
    memset(head, -1, sizeof(head));
    memset(ophead, -1, sizeof(ophead));
    scanf("%d%d%d", &n, &m, &t);
    t--;
    for (int i = 0; i < m; i++)
    {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        a--;
        b--;
        edge[tot].next = head[a];
        head[a] = tot;
        edge[tot].v = b;
        edge[tot].w = c;
        tot++;
        opedge[optot].next = ophead[b];
        ophead[b] = optot;
        opedge[optot].v = a;
        opedge[optot].w = c;
        optot++;
    }
}

void dijkstra(int head[], Edge edge[], int len[])
{
    bool visited[maxn];

    memset(visited, 0, sizeof(visited));
    len[t] = 0;
    while (1)
    {
        int best = inf, besti = -1;
        for (int i = 0; i < n; i++)
        {
            if (len[i] < best && !visited[i])
            {
                best = len[i];
                besti = i;
            }
        }
        if (besti == -1)
            break;
        visited[besti] = true;
        for (int i = head[besti]; i != -1; i = edge[i].next)
        {
            int v = edge[i].v;
            int w = edge[i].w;
            if (len[v] > len[besti] + w)
                len[v] = len[besti] + w;
        }
    }
}

int main()
{
    //freopen("D:\\t.txt", "r", stdin);
    init();
    for (int i = 0; i < n; i++)
    {
        len[i] = oplen[i] = inf;
    }
    dijkstra(head, edge, len);
    dijkstra(ophead, opedge, oplen);
    int best = 0;
    for (int i = 0; i < n; i++)
        if (best < len[i] + oplen[i])
            best = len[i] + oplen[i];
    printf("%d\n", best);
    return 0;
}