mirror of
https://git.sb/baoshuo/OI-codes.git
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154 lines
3.1 KiB
C++
154 lines
3.1 KiB
C++
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#include <iostream>
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#include <vector>
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using std::cin;
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using std::cout;
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using std::endl;
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const int N = 100005;
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int n, q, u, v;
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char op;
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std::vector<int> g[N];
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// Heavy Path Decomposition
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int cnt, id[N], rid[N], fa[N], dep[N], son[N], siz[N], top[N];
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void dfs1(int, int);
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void dfs2(int, int);
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void modify_path(int);
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int query_path(int);
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// Segment Tree
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void pushup(int);
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void build(int, int, int);
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void modify(int, int, int);
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int query(int, int, int);
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int main() {
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cin >> n >> q;
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for (int i = 1; i < n; i++) {
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cin >> u >> v;
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g[u].push_back(v);
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g[v].push_back(u);
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}
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dfs1(1, 1);
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dfs2(1, 1);
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build(1, 1, n);
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modify_path(1);
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while (q--) {
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cin >> op >> u;
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if (op == 'C') {
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modify_path(u);
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} else {
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cout << query_path(u) << endl;
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}
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}
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return 0;
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}
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// === Heavy Path Decomposition ===
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void dfs1(int u, int f) {
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fa[u] = f;
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siz[u] = 1;
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dep[u] = dep[f] + 1;
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for (int v : g[u]) {
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if (v == f) continue;
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dfs1(v, u);
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siz[u] += siz[v];
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if (siz[son[u]] < siz[v]) son[u] = v;
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}
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}
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void dfs2(int u, int t) {
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id[u] = ++cnt;
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top[u] = t;
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if (!son[u]) return;
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dfs2(son[u], t);
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for (int v : g[u]) {
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if (v == fa[u]) continue;
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if (v == son[u]) continue;
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dfs2(v, v);
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}
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}
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inline void modify_path(int u) {
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modify(1, id[u], u);
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}
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int query_path(int u) {
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while (top[u] != 1) {
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int t = query(1, id[top[u]], id[u]);
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if (t != -1) return t;
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u = fa[top[u]];
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}
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int t = query(1, 1, id[u]);
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if (t == -1) return 1;
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return t;
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}
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// === Segment Tree ===
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struct node {
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int l, r, d;
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node()
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: l(0), r(0), d(-1) {}
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node(int _l, int _r)
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: l(_l), r(_r), d(-1) {}
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} tr[N << 2];
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inline void pushup(int u) {
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node &root = tr[u], &left = tr[u << 1], &right = tr[u << 1 | 1];
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if (left.d != -1 && right.d != -1) {
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if (dep[left.d] > dep[right.d]) {
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root.d = left.d;
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} else {
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root.d = right.d;
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}
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} else if (left.d != -1) {
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root.d = left.d;
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} else if (right.d != -1) {
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root.d = right.d;
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} else {
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root.d = -1;
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}
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}
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void build(int u, int l, int r) {
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tr[u] = node(l, r);
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if (l == r) return;
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int mid = l + r >> 1;
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build(u << 1, l, mid);
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build(u << 1 | 1, mid + 1, r);
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}
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void modify(int u, int x, int k) {
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if (tr[u].l == tr[u].r) {
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tr[u].d = k;
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return;
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}
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int mid = tr[u].l + tr[u].r >> 1;
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if (x <= mid) {
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modify(u << 1, x, k);
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} else {
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modify(u << 1 | 1, x, k);
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}
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pushup(u);
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}
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int query(int u, int l, int r) {
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if (l <= tr[u].l && tr[u].r <= r) return tr[u].d;
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int mid = tr[u].l + tr[u].r >> 1;
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int left = -1, right = -1;
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if (l <= mid) left = query(u << 1, l, r);
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if (r > mid) right = query(u << 1 | 1, l, r);
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if (left != -1 && right != -1) {
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if (dep[left] > dep[right]) return left;
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return right;
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}
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if (left != -1) return left;
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if (right != -1) return right;
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return -1;
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}
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