[Luogu 1073] NOIP2009 最優貿易

<題目連結>

分層圖，跑最長路。

真不是我戀舊，是我寫的 Dijkstra 求不出正確的最長路，我才鋌而走險寫 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; 
}