Submission #1791038

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Source Code Expand

import java.util.*;
import java.io.*;

public class Main {
    private static IO io = new IO();
    
    public static void main(String[] args) {
        int n = io.nextInt();
        List<ArrayList<Integer>> list = new ArrayList<>();
        for (int i = 0; i < n; i++) list.add(new ArrayList<>());
        for (int i = 0; i < n - 1; i++) {
            int a = io.nextInt()-1;
            int b = io.nextInt()-1;
            list.get(a).add(b);
            list.get(b).add(a);
        }

        int q = io.nextInt();
        Deque<int[]> que = new ArrayDeque<>();
        boolean v[] = new boolean[n];
        for (int i = 0; i < q; i++) {
            int a = io.nextInt()-1;
            int b = io.nextInt()-1;
            Arrays.fill(v, false);
            v[a] = true;
            que.clear();
            que.offer(new int[] {0, a});

            // Q=1ならaからbまで辿って辺を数えられる
            // O(NQ)だから制限なしだとTLE
            int ans = 0;
            while (!que.isEmpty()) {
                int poll[] = que.poll();
                int dis = poll[0];
                int now = poll[1];
                if (now==b) {
                    ans = dis;
                    break;
                }
                int ways = list.get(now).size();
                for (int j = 0; j < ways; j++) {
                    int to = list.get(now).get(j);
                    if (!v[to]) {
                        que.offer(new int[] {dis+1, to});
                        v[to] = true;
                    }
                }
            }
            System.out.println(ans+1);
        }
    }

    static class IO extends PrintWriter {
        private final InputStream in;
        private final byte[] buffer = new byte[1024];
        private int ptr = 0;
        private int buflen = 0;

        IO() {
            this(System.in);
        }

        IO(InputStream source) {
            super(System.out);
            this.in = source;
        }

        boolean hasNextByte() {
            if (ptr < buflen) return true;
            else {
                ptr = 0;
                try {
                    buflen = in.read(buffer);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (buflen <= 0) return false;
            }
            return true;
        }
        int readByte() {
            if (hasNextByte()) return buffer[ptr++];
            else return -1;
        }
        boolean isPrintableChar(int c) {return 33<=c &&c <=126;}
        void skipUnprintable() {while(hasNextByte() && !isPrintableChar(buffer[ptr]))ptr++;}
        boolean hasNext() {
            skipUnprintable();
            return hasNextByte();
        }

        long nextLong() {
            if (!hasNext()) throw new NoSuchElementException();
            long n = 0;
            boolean minus = false;
            int b = readByte();
            if (b == '-') {
                minus = true;
                b = readByte();
            }
            if (b < '0' || '9' < b) throw new NumberFormatException();
            while (true) {
                if ('0' <= b && b <= '9') {
                    n *= 10;
                    n += b - '0';
                } else if (b == -1 || !isPrintableChar(b)) return minus ? -n : n;
                else throw new NumberFormatException();
                b = readByte();
            }
        }

        int nextInt() {
            long nl = nextLong();
            if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
            return (int) nl;
        }

        public void close() {
            super.close();
            try {
                in.close();
            } catch (IOException ignored) {
            }
        }
    }
}

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