FJ的字符串

还是递归  很简单，多看多做几个递归的就会了

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = Integer.parseInt(sc.nextLine());
		String s = "";
		s = A(s, 0, n);
		System.out.println(s);

	}
	
	public static String A(String s,int i,int n){
		if(i == n-1 ){//（n-1）是因为要对应序号  比如A1 = “A”+0；
			s = s+(char)((n-1)+'A')+s;
			return s;
		}else{
			s = s+(char)(i+'A')+s;
			i++;
			s = A(s, i, n);
		}
		
		return s;
	}

}