[Luogu 1073] NOIP2009 最优贸易

[Luogu 1073] NOIP2009 最优贸易

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分层图，跑最长路。

真不是我恋旧，是我写的 Dijkstra 求不出正确的最长路，我才铤而走险写 SPFA 的…

#include <algorithm>
#include <cstdio>
#include <cstring>
#include <queue>

const int MAXN = 100010; 

int n, m, value[MAXN]; 

struct Graph
{
    struct Edge
    {
        int to, w;
        Edge *next;
        Edge(int to, int w, Edge* next): to(to), w(w), next(next) {}
        ~Edge(void)
        {
            if(next != NULL)
                delete next;
        }
    }*head[MAXN * 3];
    Graph(int n)
    {
        std :: fill(head, head + n * 3 + 1, (Edge*)NULL);
        head[n] = new Edge(0, 0, head[n]);
        head[n * 3] = new Edge(0, 0, head[n * 3]);
    }
    ~Graph(void)
    {
        for(int i = 0; i <= n * 3; ++i)
            delete head[i];
    }
    void AddEdge(int u, int v)
    {
        head[u] = new Edge(v, 0, head[u]);
        head[u] = new Edge(v + n, -value[u], head[u]);
        head[u + n] = new Edge(v + n, 0, head[u + n]);
        head[u + n] = new Edge(v + n * 2, value[u], head[u + n]);
        head[u + n * 2] = new Edge(v + n * 2, 0, head[u + n * 2]);
    }
}*G; 

namespace SPFA
{
    bool exist[MAXN * 3];
    int dist[MAXN * 3];
    std :: queue<int> Q;
    void SPFA(void)
    {
        memset(dist, 0xc0, sizeof dist);
        Q.push(1);
        exist[1] = true;
        dist[1] = 0;
        while(!Q.empty())
        {
            int u = Q.front(), v;
            Q.pop();
            exist[u] = false;
            for(Graph :: Edge *i = G -> head[u]; i != NULL; i = i -> next)
                if(dist[v = i -> to] < dist[u] + i -> w)
                {
                    if(!exist[v])
                        Q.push(v);
                    dist[v] = dist[u] + i -> w;
                }
        }
    }
}

int main(void)
{
    scanf("%d %d", &n, &m);
    G = new Graph(n);
    for(int i = 1; i <= n; ++i)
        scanf("%d", &value[i]);
    for(int i = 1, x, y, z; i <= m; ++i)
    {
        scanf("%d %d %d", &x, &y, &z);
        G -> AddEdge(x, y);
        if(z == 2)
            G -> AddEdge(y, x);
    }
    SPFA :: SPFA();
    printf("%d\n", SPFA :: dist[0]);
    delete G;
    return 0;
}