POJ3159（SPFA+链式前向星存图）

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反思：本题图是密集图，所以用queue的时候的log的复杂度就不能忽略了，而且点数不是很多，考虑到这个，就需要用一个数组来模拟操作，来降低复杂度，把log的复杂度变为线性的，其他的没什么了。

#include <iostream>
#include <queue>
#include <cstdio>
#include <map>
#include <cstring>
#include <stack>
#include <string>
#include <vector>
#include <cmath>

using namespace std;

const int INF = 1 << 30;
const int maxn = 30010;
const int maxm = 150010;

struct Edge
{
    int v, w;
    int next;
    Edge(){}
    Edge(int vv, int ww, int nn) : v(vv), w(ww), next(nn) {}
};

int n, m;
int head[maxn];
Edge e[maxm];
int dis[maxn];
int q[maxn];
int vis[maxn];
int cnt;
int top;

void Init()
{
    top = 0;
    cnt = 0;
    memset (head, -1, sizeof(head));
    for (int i = 1; i<= n; i++) {
        dis[i] = INF;
    }
}

void add(int u, int v, int w)
{
    e[cnt] = Edge(v, w, head[u]);
    head[u] = cnt++;
}

void SPFA(int v)
{
    memset (vis, 0, sizeof(vis));
    q[top++] = v;
    dis[v] = 0;
    vis[v] = 1;
    while (top != 0) {
        int t = q[--top];
        vis[t] = 0;
        for (int i = head[t]; i != -1; i = e[i].next) {
            Edge tmp = e[i];
            int md = tmp.w + dis[t];
            if (md < dis[tmp.v]) {
                dis[tmp.v] = md;
                if (!vis[tmp.v]) {
                    vis[tmp.v] = 1;
                    q[top++] = tmp.v;
                }
            }
        }
    }
}

int main()
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
    //freopen("out.txt", "w", stdout);
    #endif // ONLINE_JUDGE
    scanf ("%d%d", &n, &m);
    Init ();
    for (int i = 0; i < m; i++) {
        int a, b, c;
        scanf ("%d%d%d", &a, &b, &c);
        add(a, b, c);
    }
    SPFA (1);
    printf ("%d", dis[n]);
    return 0;
}