spfa邻接矩阵形式

int cost[MAX_V][MAX_V];
int d[MAX_V];
bool used[MAX_V];
int p[MAX_V];
int in[MAX_V];

void init() {
    for(int i = 0; i <= N; i++) {
        cost[i][i] = 0;
        for(int j = 0; j < i; j++) {
            cost[i][j] = cost[j][i] = INF;
        }
        used[i] = false;
        d[i] = INF;
        p[i] = -1;
        in[i] = 0;
    }
}

bool spfa(int s) {
    queue que;
    que.push(s);
    used[s] = true;
    d[s] = 0;
    in[s]++;
    while(!que.empty()) {
        int u = que.front();
        que.pop();
        used[u] = false;
        for(int v = 1; v <= N; v++) {
            if(d[v] > d[u] + cost[u][v]) {
                d[v] = d[u] + cost[u][v];
                if(!used[v]) {
                    que.push(v);
                    used[v] = true;
                    in[v]++;
                    if(in[v] >= N)
                        return false;
                }
            }
        }
    }
    return true;
}