C10第8章 SPFA 算法

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3 3
1 2 5
2 3 5
3 1 2

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#include <iostream>
#include <cstring>
#include <queue>
using namespace std;
const int N = 1e3 + 9;
const int M = 1e4 + 9;
struct edge {
    int v, w, next;
    edge() {}
    edge(int _v, int _w, int _next) {
        v = _v;
        w = _w;
        next = _next;
    }
} e[M << 1];
int head[N], len;
void init() {
    memset(head, -1, sizeof(head));
    len = 0;
}
void add(int u, int v, int w) {
    e[len] = edge(v, w, head[u]);
    head[u] = len++;
}
void add2(int u, int v, int w) {
    add(u, v, w);
    add(v, u, w);
}


int n, m;
int dis[N];
bool vis[N];

void spfa(int u) {
    memset(vis, false, sizeof(vis));
    vis[u] = true;
    memset(dis, 0x3f, sizeof(dis));
    dis[u] = 0;
    queue<int> q;
    q.push(u);
    while (!q.empty()) {
        u = q.front();
        q.pop();
        vis[u] = false;
        for (int j = head[u]; ~j; j = e[j].next) {
            int v = e[j].v;
            int w = e[j].w;
            if (dis[v] > dis[u] + w) {
                dis[v] = dis[u] + w;
                if (!vis[v]) {
                    q.push(v);
                    vis[v] = true;
                }
            }
        }
    }
}

int main() {
    init();
    int u, v, w;
    cin >> n >> m;
    while (m--) {
        cin >> u >> v >> w;
        add2(u, v, w);
    }

    spfa(1);
    cout << dis[n] << endl;

    return 0;
}