KuangBing线段树--分配任务 && DFS序

分析：

树形结构转换为线性结构(DFS序)

DFS序看这里

#include <bits/stdc++.h>
using namespace std;
#define mst(x, y) memset(x, y, sizeof x)
#define endl '\n'
#define INF LONG_LONG_MAX
#define pb push_back
#define x first
#define y second
#define int long long
#define Lson u << 1, l, mid
#define Rson u << 1 | 1, mid + 1, r
#define FAST ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
const int N = 50010, MOD = 1e9 + 7;
const double EPS = 1e-6;
typedef pair<int, int> PII;
typedef unordered_map<int, int> Ump;
int T;
int n, m;
vector<int> g[N];
int in[N], out[N];
bool st[N];
int root, tamp;
int Case;
struct Node
{
    int l, r;
    int f, lazy;
} tr[N << 2];
void dfs(int u, int fa)
{
    if (u == fa)
        return;
    in[u] = ++tamp;
    for (auto t : g[u])
        dfs(t, u);
    out[u] = tamp;
}
void build(int u, int l, int r)
{
    if (l == r)
        tr[u] = {l, r, -1, -1};
    else
    {
        tr[u] = {l, r, -1, -1};
        int mid = l + r >> 1;
        build(Lson), build(Rson);
    }
}
void pushdown(int u)
{
    if (tr[u].lazy != -1)
    {
        tr[u << 1].lazy = tr[u << 1 | 1].lazy = tr[u].lazy;
        tr[u << 1].f = tr[u << 1 | 1].f = tr[u].lazy;
        tr[u].lazy = -1;
    }
}
void modify(int u, int l, int r, int k)
{
    if (tr[u].l >= l && tr[u].r <= r)
    {
        tr[u].f = tr[u].lazy = k;
    }
    else
    {
        pushdown(u);
        int mid = tr[u].l + tr[u].r >> 1;
        if (l <= mid)
            modify(u << 1, l, r, k);
        if (r > mid)
            modify(u << 1 | 1, l, r, k);
    }
}
Node query(int u, int pos)
{
    if (tr[u].l == pos && tr[u].r == pos)
        return tr[u];
    else
    {
        pushdown(u);
        int mid = tr[u].l + tr[u].r >> 1;
        if (pos <= mid)
            return query(u << 1, pos);
        else
            return query(u << 1 | 1, pos);
    }
}
void solve()
{
    tamp = 0;
    Case++;
    cout << "Case #" << Case << ":" << endl;
    mst(st, false);
    cin >> n;
    build(1, 1, n);
    for (int i = 1; i <= n; i++)
        g[i].clear();
    for (int i = 1, u, v; i < n; i++)
    {
        cin >> u >> v;
        g[v].pb(u);
        st[u] = true;
    }

    for (int i = 1; i <= n; i++)
        if (!st[i])
            root = i;

    dfs(root, -1);

    cin >> m;
    string op;
    while (m--)
    {
        int a, b;
        cin >> op;
        if (op == "C")
        {
            cin >> a;
            cout << query(1, in[a]).f << endl;
        }
        else
        {
            cin >> a >> b;
            modify(1, in[a], out[a], b);
        }
    }
}
signed main()
{
    FAST;
    // T = 1;
    cin >> T;
    while (T--)
        solve();
    return 0;
}

相反的：由DFS序推出树形结构

树上基因重组

#include <bits/stdc++.h>
using namespace std;
#define mst(x, y) memset(x, y, sizeof x)
#define endl '\n'
#define INF LONG_LONG_MAX
#define pb push_back
#define x first
#define y second
#define int long long
#define Lson u << 1, l, mid
#define Rson u << 1 | 1, mid + 1, r
#define FAST ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
const int N = 2000010, MOD = 1e9 + 7;
const double EPS = 1e-6;
typedef pair<int, int> PII;
typedef unordered_map<int, int> Ump;
int T;
int n;
int idx = 1;
int a[N], w[N];
struct P
{
    int u, v;
} p[N];
bool cmp(P a, P b)
{
    if (a.u == b.u)
        return a.v < b.v;
    return a.u < b.u;
}
void dfs(int u)
{
    w[u]--;
    while (w[u])
    {
        int t = a[++idx];
        p[idx - 1] = {u, t};
        w[u] -= w[t];
        dfs(t);
    }
}
void solve()
{
    cin >> n;
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    for (int i = 1; i <= n; i++)
        cin >> w[i];

    dfs(a[1]);

    for (int i = 1; i < idx; i++)
    {
        if (p[i].u > p[i].v)
            swap(p[i].u, p[i].v);
    }
    sort(p + 1, p + idx, cmp);

    for (int i = 1; i < idx; i++)
        cout << p[i].u << " " << p[i].v << endl;
}
signed main()
{
    FAST;
    T = 1;
    // cin >> T;
    while (T--)
        solve();
    return 0;
}