Language: Java

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.StringJoiner;
import java.util.function.IntUnaryOperator;
import java.util.function.LongUnaryOperator;
import java.util.*;

public class Main {
    public static class Edge {
      int idx;
      int node;
      public Edge(int n, int i) {
        this.idx = i;
        this.node = n;
      }
    }
    static In in = new In();
    static Out out = new Out();
    static long mod = 1000000007;
    static long inf = 0xfffffffffffffffL;

    void solve() {
        int n = in.nextInt();

        Map<Integer, List<Edge>> graph = new HashMap<>();
        for(int i = 1; i <= n; i++)
            graph.put(i, new ArrayList<>());

        for(int i = 0; i < n - 1; i++) {
            int v = in.nextInt();
            int u = in.nextInt();
            graph.get(v).add(new Edge(u, i));
            graph.get(u).add(new Edge(v, i));
        }

        int cnt = 0;
        for(List<Edge> adjs : graph.values())
            cnt = Math.max(cnt, adjs.size());
        out.println(cnt);
        
        int[] colors = new int[n-1];
        Map<Integer, Set<Integer>> usedColor = new HashMap<>();
        for(int i = 1; i <= n; i++) usedColor.put(i, new HashSet<>());
        Queue<Integer> queue = new LinkedList<>();
        Set<Integer> visited = new HashSet<>();
        queue.offer(1);
        visited.add(1);
        while(!queue.isEmpty()) {
          int node = queue.poll();
          for(Edge e : graph.get(node)) {
            if(visited.contains(e.node)) continue;
            int c = 1;
            while(usedColor.get(node).contains(c) || usedColor.get(e.node).contains(c)) c++;
            if(colors[e.idx] == 0)
                colors[e.idx] = c;
            usedColor.get(node).add(c);
            usedColor.get(e.node).add(c);
            queue.offer(e.node);
            visited.add(e.node);
          }
        }
        for(int i = 0; i < colors.length; i++)
          out.println(colors[i]);
    }

    public static void main(String[]$) {
        new Main().solve();
        out.flush();
    }
}

public class In {
    private BufferedInputStream reader = new BufferedInputStream(System.in);
    private byte[] buffer = new byte[0x8000];
    private int i = 0;
    private int length = 0;

    private int read() {
        if (i == length) {
            i = 0;
            try {
                length = reader.read(buffer);
            } catch (IOException ignored) {
            }
            if (length == -1) {
                return -1;
            }
        }
        return buffer[i++];
    }

    String next() {
        StringBuilder builder = new StringBuilder();
        int b = read();
        while (b < '!' || '~' < b) {
            b = read();
        }
        while ('!' <= b && b <= '~') {
            builder.appendCodePoint(b);
            b = read();
        }
        return builder.toString();
    }

    int nextInt() {
        return (int)nextLong();
    }

    long nextLong() {
        int b = read();
        while (b < '!' || '~' < b) {
            b = read();
        }
        int i = 0;
        if (b == '-') {
            i = 1;
            b = read();
        }
        long n = 0;
        while ('0' <= b && b <= '9') {
            n = n * 10 + b - '0';
            b = read();
        }
        return i == 0 ? n : -n;
    }

    char[][] nextCharArray(int n, int m) {
        char[][] a = new char[n][m];
        for (int i = 0; i < n; i++) {
            a[i] = next().toCharArray();
        }
        return a;
    }

    int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = nextInt();
        }
        return a;
    }

    int[] nextIntArray(int n, IntUnaryOperator op) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = op.applyAsInt(nextInt());
        }
        return a;
    }

    long[] nextLongArray(int n) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = nextLong();
        }
        return a;
    }

    long[] nextLongArray(int n, LongUnaryOperator op) {
        long[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = op.applyAsLong(nextLong());
        }
        return a;
    }
}

class Out {
    private static PrintWriter out = new PrintWriter(System.out);

    void println(Object... a) {
        StringJoiner joiner = new StringJoiner(" ");
        for (Object obj : a) {
            joiner.add(String.valueOf(obj));
        }
        out.println(joiner);
    }

    void print(Object... a) {
        StringJoiner joiner = new StringJoiner(" ");
        for (Object obj : a) {
            joiner.add(String.valueOf(obj));
        }
        out.print(joiner);
    }

    void flush() {
        out.flush();
    }
}


Compiler output:
Main.java:73: error: class In is public, should be declared in a file named In.java
public class In {
       ^
1 error