//前向星struct node {    int nxt;    int val;    int lst;    node () {}    node (int next, int value) : nxt(next), val(value) {}};struct headnode {    int u;    int val;    headnode () {}    headnode (int uu, int value) : u(uu), val(value) {}    bool operator < (const headnode &a) const {        return val > a.val;    }};  // 用于优先队列而已。val是比较的值。dist[i]int dist[maxn];bool vis[maxn];node edge[maxn];int  last[maxn]void Dij(){    memset(dist, 0x3f, sizeof(dist));    memset(vis,  0,    sizeof(vis));    priority_queue
     
       pq;    pq.push(headnode(1, 0));    dist[1] = 0;    headnode now;    while (!pq.empty()) {        now = pq.top(); pq.pop();        if (vis[now.u]) continue;        vis[now.u] = true;        for (int i=last[now.u]; i!=-1; i=edge[i].lst) {            if (dist[edge[i].nxt] > edge[i].val + dist[now.u]) {                dist[edge[i].nxt] = edge[i].val + dist[now.u];                pq.push(headnode(edge[i].nxt, dist[edge[i].nxt]));            }            }    }}