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普通的SPFA：

int top;
int head[MAXN];
struct Edge {
    int v, nxt;
    int w;
} edge[MAXM];

void init() {
    top = 0;
    memset(head, -1, sizeof(head));
}

void add_edge(int u, int v, int w) {
    ++top;
    edge[top].v = v;
    edge[top].w = w;
    edge[top].nxt = head[u];
    head[u] = top;
}

bool vis[MAXN];
int cnt[MAXN];
int dis[MAXN];

queue<int>q;
bool spfa(int s, int n) {
    memset(vis, 0, sizeof(vis));
    memset(cnt, 0, sizeof(cnt));
    for(int i = 0; i < MAXN; ++i)
        dis[i] = 0x3f3f3f3f;

    while(!q.empty())
        q.pop();
    q.push(s);
    vis[s] = 1;
    cnt[s] = 1;
    dis[s] = 0;

    while(!q.empty()) {
        int u = q.front();
        q.pop();
        vis[u] = 0;
        for(int i = head[u]; i != -1; i = edge[i].nxt) {
            int v = edge[i].v;
            if(dis[v] > dis[u] + edge[i].w) {
                dis[v] = dis[u] + edge[i].w;
                if(!vis[v]) {
                    vis[v] = 1;
                    q.push(v);
                    if(++cnt[v] > n)
                        return 0;
                }
            }
        }
    }
    return 1;
}

带SLF优化的SPFA，实测在某些数据上确实会快（有人说是15%左右，但实际上貌似不止？反正抖得厉害）

int top;
int head[MAXN];
struct Edge {
    int v, nxt;
    int w;
} edge[MAXM];

void init() {
    top = 0;
    memset(head, -1, sizeof(head));
}

void add_edge(int u, int v, int w) {
    ++top;
    edge[top].v = v;
    edge[top].w = w;
    edge[top].nxt = head[u];
    head[u] = top;
}

bool vis[MAXN];
int cnt[MAXN];
int dis[MAXN];

deque<int>q;
bool spfa(int s, int n) {
    memset(vis, 0, sizeof(vis));
    memset(cnt, 0, sizeof(cnt));
    for(int i = 0; i < MAXN; ++i)
        dis[i] = 0x3f3f3f3f;

    q.clear();
    q.push_back(s);
    vis[s] = 1;
    cnt[s] = 1;
    dis[s] = 0;

    while(!q.empty()) {
        int u = q.front();
        q.pop_front();
        vis[u] = 0;
        for(int i = head[u]; i != -1; i = edge[i].nxt) {
            int v = edge[i].v;
            if(dis[v] > dis[u] + edge[i].w) {
                dis[v] = dis[u] + edge[i].w;
                if(!vis[v]) {
                    vis[v] = 1;
                    //SLF优化 据说15%~20%
                    if(!q.empty() && dis[v] >= dis[q.front()])
                        q.push_back(v);
                    else
                        q.push_front(v);
                    if(++cnt[v] > n)
                        return 0;
                }
            }
        }
    }
    return 1;
}