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142 lines (129 loc) · 4.49 KB
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package codeforces.tree_basics;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.StringTokenizer;
public final class C {
// https://codeforces.com/blog/entry/43230
public static void main(String[] args) throws IOException {
final FastScanner fs = new FastScanner();
final PrintWriter pw = new PrintWriter(System.out);
final int n = fs.nextInt();
final Map<Integer, List<Integer>> g = new HashMap<>();
for (int i = 1; i < n; i++) {
final int l = fs.nextInt() - 1;
final int r = fs.nextInt() - 1;
g.computeIfAbsent(l, v -> new ArrayList<>()).add(r);
g.computeIfAbsent(r, v -> new ArrayList<>()).add(l);
}
final int[] parents = new int[n];
final int[] depth = new int[n];
dfs(g, 0, -1, 0, parents, depth);
final TreeAncestor ta = new TreeAncestor(n, parents);
final int q = fs.nextInt();
for (int i = 0; i < q; i++) {
final int a = fs.nextInt() - 1;
final int b = fs.nextInt() - 1;
final int c = fs.nextInt();
final int lca = ta.getLca(a, b, depth);
final int left = depth[a] - depth[lca];
final int right = depth[b] - depth[lca];
if (c >= left + right) {
pw.println(b + 1);
} else if (c >= left) {
pw.println(ta.getKthAncestor(b, right - (c - left)) + 1);
} else {
pw.println(ta.getKthAncestor(a, c) + 1);
}
}
pw.flush();
}
private static void dfs(Map<Integer, List<Integer>> g, int u, int v, int d, int[] parents, int[] depth) {
parents[u] = v;
depth[u] = d;
for (int next : g.getOrDefault(u, Collections.emptyList())) {
if (next != v) {
dfs(g, next, u, d + 1, parents, depth);
}
}
}
private static final class TreeAncestor {
int h;
int[][] parents;
private TreeAncestor(int n, int[] parent) {
h = (int) (Math.log(n) / Math.log(2));
parents = new int[h + 1][n];
parents[0] = parent;
for (int i = 1; i <= h; i++) {
for (int node = 0; node < n; node++) {
final int nodeParent = parents[i - 1][node];
if (nodeParent != -1) {
parents[i][node] = parents[i - 1][nodeParent];
} else {
parents[i][node] = -1;
}
}
}
}
public int getKthAncestor(int node, int k) {
for (int i = 0; i <= h; i++) {
if ((k & (1 << i)) != 0) {
node = parents[i][node];
if (node == -1) {
return -1;
}
}
}
return node;
}
public int getLca(int u, int v, int[] depth) {
if (depth[u] < depth[v]) {
v = getKthAncestor(v, depth[v] - depth[u]);
} else {
u = getKthAncestor(u, depth[u] - depth[v]);
}
if (u == v) {
return u;
}
for (int i = h; i >= 0; i--) {
if (parents[i][u] != parents[i][v]) {
u = parents[i][u];
v = parents[i][v];
}
}
return parents[0][u];
}
}
static class FastScanner {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
StringTokenizer st = new StringTokenizer("");
String next() {
while (!st.hasMoreTokens()) {
try {
st = new StringTokenizer(br.readLine());
} catch (IOException e) {
//noinspection CallToPrintStackTrace
e.printStackTrace();
}
}
return st.nextToken();
}
int nextInt() {
return Integer.parseInt(next());
}
int[] readArray(int n) {
final int[] a = new int[n];
for (int i = 0; i < n; i++) { a[i] = nextInt(); }
return a;
}
long nextLong() {
return Long.parseLong(next());
}
}
}