Blue Bridge Cup FJ string Java

Problem Description

FJ in the sand table to write some string like this:
　　A1 = "A"
　　A2 = "ABA"
　　A3 = "ABACABA"
　　A4 = "ABACABADABACABA"
　　... ...
　　you can find out the rules and write them all columns AN it?

Input Format

Only a few: N ≤ 26.

Output Format

Please output corresponding string AN, to a newline character. Output must not contain extra space or line feed, carriage return.

Sample input

3

Sample Output

Spearheading

Thinking

The examples given topic may be found Law:
A1 = "A"
An = An-new letter. 1 + + An-1
a new letter (char) 'A' n + - 1
can be seen a recursive solution to this problem
here given two kinds of recursive and recursive disassembly method

Code

import java.util.Scanner;
public class FJString {
	public static void main(String[] args) {
		Scanner input = new Scanner(System.in);
		int n = input.nextInt();
		System.out.println(solution2(n));
		System.out.println(solution1(n));
	}
	public static String solution1(int n) { //递归法
		if(n == 1) 
			return "A";
		String insert = String.valueOf((char) ('A' + n - 1));
		return solution1(n - 1) + insert + solution1(n - 1);
		
	}
	public static String solution2(int n) {  //递推法
		String str = new String();
		for (int i = 1; i <= n; i++) {
			String insert = String.valueOf((char) ('A' + i - 1));
			String str_new = str + insert + str;
			str = str_new;
		}
		return str;
	}
}