递归基础练习

翻转字符串

public class 翻转字符串 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String s = "abcefghijk";
		System.out.println(f(s));
	}
	private static String f(String s){
		if(s.length() == 1){
			return s;
		}
		return f(s.substring(1, s.length())) + s.charAt(0);// 包左不包右
	}
}

Fibonacci数列

public class Fibonacci数列 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.println(f(6));
	}
	private static int f(int n){
		if(n == 2){
			return 1;
		}
		if(n == 1){
			return 1;
		}
		return f(n - 1) + f(n - 2);
	}
}

简单综合

public class 综合练习 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

	}

	// 阶乘
	private static int f(int n) {
		if (n == 1) {
			return 1;
		}
		return n * f(n - 1);
	}

	// 计算i - j
	private static int f1(int i, int j) {
		if (j == 1) {
			return i - 1;
		}
		return i - 1 - f1(j, 1);
	}

	// 数组求和
	private static int f2(int[] arr, int n) {
		if (n == 1) {
			return arr[0];
		}
		return arr[n - 1] + f2(arr, n - 1);
	}

	// 打印i到j
	private static void f3(int i, int j) {
		if (i == j) {
			System.out.println(i);
			return;
		}
		System.out.println(i);
		f3(i + 1, j);
	}
}