[BOJ] 11729. 하노이 탑 이동 순서

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		System.out.println((1<<n) - 1);
		StringBuilder sb = solve(n,1,3,2);
		System.out.println(sb);
	}
	
	// solve(n,from,to,by) : n개를 from에서 by를 거쳐 to로 옮기는 함수. 
	public static StringBuilder solve(int n, int from, int to, int by) {
		StringBuilder sb = new StringBuilder();
		if(n == 1) {
			sb.append(move(from, to));
			return sb;
		}
		sb.append(solve(n-1,from,by,to));
		sb.append(move(from,to));
		sb.append(solve(n-1,by, to,from));
		return sb;
	}
	
	// move(from,to) : 1개를 from에서 to로 옮기는 함수. 
	public static StringBuilder move(int from, int to) {
		StringBuilder sb = new StringBuilder(from + " " + to + "\n");
		return sb;
	}
}