Problem:
Score : 400 points

Problem Statement

Given is a tree G with N vertices.
The vertices are numbered 1 through N, and the i-th edge connects Vertex a_i and Vertex b_i.

Consider painting the edges in G with some number of colors.
We want to paint them so that, for each vertex, the colors of the edges incident to that vertex are all different.

Among the colorings satisfying the condition above, construct one that uses the minimum number of colors.

Constraints

2 \le N \le 10^5

1 \le a_i \lt b_i \le N

All values in input are integers.

The given graph is a tree.

Input

Input is given from Standard Input in the following format:

N
a_1 b_1
a_2 b_2
\vdots
a_{N-1} b_{N-1}

Output

Print N lines.

The first line should contain K, the number of colors used.

The (i+1)-th line (1 \le i \le N-1) should contain c_i, the integer representing the color of the i-th edge, where 1 \le c_i \le K must hold.

If there are multiple colorings with the minimum number of colors that satisfy the condition, printing any of them will be accepted.

Sample Input 1

3
1 2
2 3

Sample Output 1

2
1
2

Sample Input 2

8
1 2
2 3
2 4
2 5
4 7
5 6
6 8

Sample Output 2

4
1
2
3
4
1
1
2

Sample Input 3

6
1 2
1 3
1 4
1 5
1 6

Sample Output 3

5
1
2
3
4
5

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io;
use std::collections::HashMap;
use io_ext::Reader;
use parse::ParseAll;

fn main() {
    let stdin = io::stdin();
    let mut r = Reader::new(stdin.lock());
    let n: usize = r.read_line().parse().unwrap();
    let mut edges: Vec<(usize, usize)> = Vec::with_capacity(n);
    for _ in 0..(n - 1) {
        let (a, b): (usize, usize) = r.read_line().split_whitespace().parse_all();
        let (a, b) = (a - 1, b - 1);
        edges.push((a, b));
    }

    let (count, colors) = answer(&edges);
    println!("{}", count);
    for c in colors {
        println!("{}", c + 1);
    }
}

struct Tree {
    vertex: usize,
    children: Vec<Tree>,
}

impl Tree {
    fn append_undirected(&mut self, parent: usize, edges: &[Vec<usize>]) {
        for &child in &edges[self.vertex] {
            if child != parent {
                self.children.push(Tree { vertex: child, children: Vec::new() });
            }
        }

        for child in &mut self.children {
            child.append_undirected(self.vertex, edges);
        }
    }

    pub fn from_undirected(edges: &[Vec<usize>]) -> Self {
        let mut root = Tree { vertex: 0, children: Vec::new() };
        root.append_undirected(usize::max_value(), edges);
        root
    }
}

fn color(tree: &Tree, nums: &HashMap<(usize, usize), usize>, colors: &mut [usize], prev_col: usize) {
    let mut skip = false;
    for (col, child) in tree.children.iter().enumerate() {
        if col == prev_col {
            skip = true;
        }
        let col = if skip {
            col + 1
        } else {
            col
        };
        colors[nums[&(tree.vertex, child.vertex)]] = col;
        color(child, nums, colors, col);
    }
}

fn answer(edges: &[(usize, usize)]) -> (usize, Vec<usize>) {
    let n = edges.len() + 1;
    let mut undir: Vec<Vec<usize>> = vec![vec![]; n];
    for &(a, b) in edges {
        undir[a].push(b);
        undir[b].push(a);
    }
    let tree = Tree::from_undirected(&undir);

    let mut nums = HashMap::with_capacity(edges.len());
    for (n, &edge) in edges.iter().enumerate() {
        nums.insert(edge, n);
    }

    let mut colors = vec![usize::max_value(); edges.len()];

    color(&tree, &nums, &mut colors, usize::max_value());
    let count = colors.iter().map(|c| *c).max().unwrap() + 1;
    (count, colors)
}

/// A module for easy use of io.
pub mod io_ext {
    use std::io::BufRead;

    pub struct Reader<R> {
        buf: String,
        inner: R,
    }

    impl<R> Reader<R> {
        #[inline]
        pub fn new(inner: R) -> Self {
            Reader { buf: String::new(), inner: inner }
        }

        #[inline]
        pub fn into_inner(self) -> R {
            self.inner
        }
    }

    impl<R: BufRead> Reader<R> {
        #[allow(deprecated)]
        #[inline]
        pub fn read_line(&mut self) -> &str {
            self.buf.clear();
            self.inner.read_line(&mut self.buf).unwrap_or_else(|e| panic!("{}", e));
            self.buf.trim_right()
        }
    }
}

/// Parsing Iterator.
pub mod parse {
    use std::borrow::Borrow;
    use std::str::FromStr;

    pub trait FromStrIterator {
        fn from_str_iter<S: Borrow<str>, I: Iterator<Item=S>>(i: I) -> Self;
    }

    pub trait ParseAll {
        fn parse_all<F: FromStrIterator>(self) -> F;
    }

    impl<S: Borrow<str>, I: Iterator<Item=S>> ParseAll for I {
        #[inline]
        fn parse_all<F: FromStrIterator>(self) -> F {
            F::from_str_iter(self)
        }
    }

    fn parse<S: Borrow<str>, I: Iterator<Item=S>, F: FromStr>(i: &mut I) -> F {
        i.next().unwrap_or_else(|| panic!("too few strings error")).borrow().parse().unwrap_or_else(|_| panic!("parse error"))
    }

    // To avoid conflict, this is not implemented for `A` but `(A,)`.
    impl<A: FromStr> FromStrIterator for (A, ) {
        fn from_str_iter<S: Borrow<str>, I: Iterator<Item=S>>(mut i: I) -> Self {
            let a = parse(&mut i);
            if i.next().is_some() {
                panic!("too many strings error");
            }
            (a, )
        }
    }

    impl<A: FromStr, B: FromStr> FromStrIterator for (A, B) {
        fn from_str_iter<S: Borrow<str>, I: Iterator<Item=S>>(mut i: I) -> Self {
            let a = parse(&mut i);
            let b = parse(&mut i);
            if i.next().is_some() {
                panic!("too many strings error");
            }
            (a, b)
        }
    }

    impl<A: FromStr, B: FromStr, C: FromStr> FromStrIterator for (A, B, C) {
        fn from_str_iter<S: Borrow<str>, I: Iterator<Item=S>>(mut i: I) -> Self {
            let a = parse(&mut i);
            let b = parse(&mut i);
            let c = parse(&mut i);
            if i.next().is_some() {
                panic!("too many strings error");
            }
            (a, b, c)
        }
    }

    impl<T: FromStr> FromStrIterator for Vec<T> {
        fn from_str_iter<S: Borrow<str>, I: Iterator<Item=S>>(i: I) -> Self {
            i.map(|s| s.borrow().parse().unwrap_or_else(|_| panic!("parse error"))).collect()
        }
    }
}

pub mod modulo {
    /// Returns `x` + `y` mod `modulo`.
    ///
    /// `x < modulo` and `y < modulo` must hold.
    #[inline]
    pub fn add(x: u32, y: u32, modulo: u32) -> u32 {
        debug_assert!(modulo > 0);
        debug_assert!(x < modulo && y < modulo);
        let sum = x as u64 + y as u64;
        if sum <= modulo as u64 {
            sum as u32
        } else {
            (sum as u32).wrapping_sub(modulo)
        }
    }

    /// Returns `x` - `y` mod `modulo`.
    ///
    /// `x < modulo` and `y < modulo` must hold.
    #[inline]
    pub fn sub(x: u32, y: u32, modulo: u32) -> u32 {
        debug_assert!(0 < modulo);
        debug_assert!(x < modulo && y < modulo);
        if x >= y {
            x - y
        } else {
            modulo + x - y
        }
    }

    /// Returns `x` * `y` mod `modulo`.
    #[inline]
    pub fn mul(x: u32, y: u32, modulo: u32) -> u32 {
        ((x as u64 * y as u64) % modulo as u64) as u32
    }

    /// Returns `x`^ `y` mod `modulo`.
    pub fn pow(x: u32, mut y: u32, modulo: u32) -> u32 {
        debug_assert!(0 < modulo);
        let mut p = x;
        let mut ret = 1;

        while y != 0 {
            if y & 1 == 1 {
                ret = mul(ret, p, modulo);
            }
            p = mul(p, p, modulo);
            y >>= 1;
        }
        ret
    }

    fn is_prime(x: u32) -> bool {
        let sqrt = (x as f32).sqrt() as u32;
        for factor in 2..sqrt {
            if x % factor == 0 {
                return false;
            }
        }
        true
    }

    /// Returns 1 / `x`.
    ///
    /// `modulo` must be a prime number.
    #[inline]
    fn reciprocal(x: u32, modulo: u32) -> u32 {
        debug_assert!(0 < modulo && is_prime(modulo));
        pow(x, modulo - 2, modulo)
    }

    /// Returns `x` / `y` mod `modulo`.
    ///
    /// `modulo` must be a prime number.
    #[inline]
    pub fn div(x: u32, y: u32, modulo: u32) -> u32 {
        debug_assert!(0 < modulo && is_prime(modulo));
        mul(x, reciprocal(y, modulo), modulo)
    }

    /// Returns `n`P`k` mod `modulo`.
    pub fn perm(n: u32, k: u32, modulo: u32) -> u32 {
        let mut p = 1;
        for i in 0..k {
            p = mul(p, n - i, modulo);
        }
        p
    }

    /// Returns `n`C`k` mod `modulo`.
    pub fn comb(n: u32, k: u32, modulo: u32) -> u32 {
        let num = perm(n, k, modulo);
        let mut den = 1;
        for i in 0..k {
            den = mul(den, i + 1, modulo);
        }
        div(num, den, modulo)
    }
}