Language: C++

//https://atcoder.jp/contests/abc146/tasks/abc146_d

#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef long double ld; 
typedef double db; 
typedef string str; 

typedef pair<int, int> pi;
typedef pair<ll,ll> pl; 
typedef pair<ld,ld> pd; 

typedef vector<int> vi; 
typedef vector<ll> vl;
typedef vector<ld> vd; 
typedef vector<str> vs; 
typedef vector<pi> vpi;
typedef vector<pl> vpl; 

#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)

#define sz(x) (int)x.size()
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x) 
#define rsz resize
#define ins insert 

#define mp make_pair
#define pb push_back
#define eb emplace_back 
#define f first
#define s second
#define lb lower_bound 
#define ub upper_bound 

const int MOD = 1e9+7; // 998244353; // = (119<<23)+1
const int MX = 2e5+5;
const ll INF = 1e18; 
const ld PI = 4*atan((ld)1); 

template<class T> bool ckmin(T& a, const T& b) { 
	return a > b ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { 
	return a < b ? a = b, 1 : 0; }

mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());

namespace input {
	template<class T> void re(complex<T>& x);
	template<class T1, class T2> void re(pair<T1,T2>& p);
	template<class T> void re(vector<T>& a);
	template<class T, size_t SZ> void re(array<T,SZ>& a);

	template<class T> void re(T& x) { cin >> x; }
	void re(double& x) { string t; re(t); x = stod(t); }
	void re(ld& x) { string t; re(t); x = stold(t); }
	template<class T, class... Ts> void re(T& t, Ts&... ts) { 
		re(t); re(ts...); 
	}

	template<class T> void re(complex<T>& x) { T a,b; re(a,b); x = cd(a,b); }
	template<class T1, class T2> void re(pair<T1,T2>& p) { re(p.f,p.s); }
	template<class T> void re(vector<T>& a) { F0R(i,sz(a)) re(a[i]); }
	template<class T, size_t SZ> void re(array<T,SZ>& a) { F0R(i,SZ) re(a[i]); }
}

using namespace input;

namespace output {
	void pr(int x) { cout << x; }
	void pr(long x) { cout << x; }
	void pr(ll x) { cout << x; }
	void pr(unsigned x) { cout << x; }
	void pr(unsigned long x) { cout << x; }
	void pr(unsigned long long x) { cout << x; }
	void pr(float x) { cout << x; }
	void pr(double x) { cout << x; }
	void pr(ld x) { cout << x; }
	void pr(char x) { cout << x; }
	void pr(const char* x) { cout << x; }
	void pr(const string& x) { cout << x; }
	void pr(bool x) { pr(x ? "true" : "false"); }
	template<class T> void pr(const complex<T>& x) { cout << x; }
	
	template<class T1, class T2> void pr(const pair<T1,T2>& x);
	template<class T> void pr(const T& x);
	
	template<class T, class... Ts> void pr(const T& t, const Ts&... ts) { 
		pr(t); pr(ts...); 
	}
	template<class T1, class T2> void pr(const pair<T1,T2>& x) { 
		pr("{",x.f,", ",x.s,"}"); 
	}
	template<class T> void pr(const T& x) { 
		pr("{"); // const iterator needed for vector<bool>
		bool fst = 1; for (const auto& a: x) pr(!fst?", ":"",a), fst = 0; 
		pr("}");
	}
	
	void ps() { pr("\n"); } // print w/ spaces
	template<class T, class... Ts> void ps(const T& t, const Ts&... ts) { 
		pr(t); if (sizeof...(ts)) pr(" "); ps(ts...); 
	}
	
	void pc() { pr("]\n"); } // debug w/ commas
	template<class T, class... Ts> void pc(const T& t, const Ts&... ts) { 
		pr(t); if (sizeof...(ts)) pr(", "); pc(ts...); 
	}
	#define dbg(x...) pr("[",#x,"] = ["), pc(x);
}

template<class T> struct modular {
	T val; 
	explicit operator T() const { return val; }
	modular() { val = 0; }
	modular(const ll& v) { 
		val = (-MOD <= v && v <= MOD) ? v : v % MOD;
		if (val < 0) val += MOD;
	}
	// friend ostream& operator<<(ostream& os, const modular& a) { return os << a.val; }
	friend void pr(const modular& a) { pr(a.val); }
	friend void re(modular& a) { ll x; re(x); a = modular(x); }
   
	friend bool operator==(const modular& a, const modular& b) { 
		return a.val == b.val; }
	friend bool operator!=(const modular& a, const modular& b) { 
		return !(a == b); }
	friend bool operator<(const modular& a, const modular& b) { 
		return a.val < b.val; }

	modular operator-() const { return modular(-val); }
	modular& operator+=(const modular& m) { 
		if ((val += m.val) >= MOD) val -= MOD; 
		return *this; }
	modular& operator-=(const modular& m) { 
		if ((val -= m.val) < 0) val += MOD; 
		return *this; }
	modular& operator*=(const modular& m) { 
		val = (ll)val*m.val%MOD; return *this; }
	friend modular pow(modular a, ll p) {
		modular ans = 1; 
		for (; p; p /= 2, a *= a) if (p&1) ans *= a;
		return ans;
	}
	friend modular inv(const modular& a) { 
		assert(a != 0); return pow(a,MOD-2); 
	}
	modular& operator/=(const modular& m) { 
		return (*this) *= inv(m); }
	
	friend modular operator+(modular a, const modular& b) { 
		return a += b; }
	friend modular operator-(modular a, const modular& b) { 
		return a -= b; }
	friend modular operator*(modular a, const modular& b) { 
		return a *= b; }
	
	friend modular operator/(modular a, const modular& b) { 
		return a /= b; }
};

typedef modular<int> mi;
typedef pair<mi,mi> pmi;
typedef vector<mi> vmi;
typedef vector<pmi> vpmi;

int ans = 0;
vpi edges;
map<pair<int, int>, int> colors;
vi adj[100000];
int n;

void dfs(int v, int p){
	//ps(v+1, p+1);
	int used = -1;
	if(p!=-1) used = colors[{v, p}];
	int cur = 1;
	ans = max(ans, sz(adj[v]));
	trav(i, adj[v]){
		if(i == p) continue;
		if(cur == used) cur++;
		colors[{i, v}] = cur;
		colors[{v, i}] = cur;
		dfs(i, v);
		cur++;
	}
}

int main() {
	cin.sync_with_stdio(0); cin.tie(0); 
	// you should actually read the stuff at the bottom
	//freopen("a.in", "r", stdin);
	re(n);
	F0R(i, n-1){
		int a, b; re(a, b); --a;--b;
		adj[a].pb(b);
		adj[b].pb(a);
		edges.pb({a, b});
		edges.pb({b, a});
	}
	// F0R(i, n){
	// 	pr(i+1, ": ");
	// 	trav(a, adj[i]) pr(a+1, ", ");
	// 	ps();
	// }
	dfs(0, -1);
	ps(ans);
	trav(a, edges){
		ps(colors[a]);
	}
}

/* stuff you should look for
	* int overflow, array bounds
	* special cases (n=1?), slow multiset operations
	* do smth instead of nothing and stay organized
*/

Compiler output:
a.cc: In function 'int main()':
a.cc:213:9: error: 'ps' was not declared in this scope; did you mean 'output::ps'?
  213 |         ps(ans);
      |         ^~
      |         output::ps
a.cc:107:45: note: 'output::ps' declared here
  107 |         template<class T, class... Ts> void ps(const T& t, const Ts&... ts) {
      |                                             ^~