模板 树链剖分BFS版本

//点和线段树都从1开始
//边使用vector
vector<int> G[maxn];

int dfs_clock,que[maxn*2],num[maxn],iii[maxn],b[maxn],a[maxn],top[maxn],deep[maxn],fa[maxn],idx[maxn];
//采用静态链表
//a[i]   是初始时树上每个点的权值
//b[i]   是经过bfs后每个点的权值
//idx[i] 是每个点在全局线段树中的下标

void build_List()
{
    int ft = 0, rear = 0;
    que[rear++] = 1;
    fa[1] = 0;
    deep[1] = 1;
    while(ft < rear)
    {
        int u = que[ft++];
        for(int i = 0; i < G[u].size(); i++)
        {
            int v = G[u][i];
            if(v == fa[u]) continue;
            fa[v] = u;
            que[rear++] = v;
            deep[v] = deep[u]+1;
        }
    }
    memset(num, 0, sizeof num);
    for(int i = n-1; i >= 0; i--)
    {
        int u = que[i];
        num[u]++;
        num[fa[u]] += num[u];
    }
    for(int i = 1; i <= n; i++)
    {
        for(int j = 1; j < G[i].size(); j++) if(G[i][j] != fa[i])
                if(G[i][0] == fa[i] || num[G[i][j]] > num[G[i][0]])
                    swap(G[i][0], G[i][j]);
    }
    top[1] = 1;
    for(int i = 1; i < n; i++)
    {
        int u = que[i];
        if(G[fa[u]][0] == u) top[u] = top[fa[u]];
        else top[u] = u;
    }
    memset(iii, 0, sizeof iii);
    ft = 0;
    dfs_clock = 0;
    que[++ft] = 1;
    idx[1] = ++dfs_clock;
    b[1] = a[1];
    while(ft)
    {
        int u = que[ft];
        if(iii[u] >= G[u].size()) ft--;
        else if(G[u][iii[u]] == fa[u]) iii[u]++;
        else
        {
            int v = G[u][iii[u]];
            que[++ft] = v;
            idx[v] = ++dfs_clock;
            b[idx[v]] = a[v];
            iii[u]++;
        }
    }
}