java递归算法实例

本文来自java入门教程栏目,文中通过实例为大家展示了递归算法的实现过程,希望可以帮助到大家。实现递归算法需要掌握三个要素,分别是:1、明确终止条件;2、给出递归终止时的处理方法;3、提取重复的逻辑。

java递归算法实例

递归三要素:

1、明确递归终止条件;

2、给出递归终止时的处理办法;

3、提取重复的逻辑,缩小问题规模。

1、1+2+3+…+n

import java.util.Scanner;

public class Recursion {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        System.out.println(sum(n));
    }

    public static int sum(int n) {
        if(n == 1) {
            return n;
        }
        else {
            return n + sum(n-1);
        }
    }
}
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2、1 * 2 * 3 * … * n

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此代码由Java架构师必看网-架构君整理
import java.util.Scanner; public class Recursion { public static void main(String[] args) { Scanner in = new Scanner(System.in); int n = in.nextInt(); System.out.println(multiply(n)); } public static int multiply(int n) { if(n == 1) { return n; } else { return n*multiply(n-1); } } }

3、斐波那契数列

前两项均为1,第三项开始,每一项都等于前两项之和。即:1,1,2,3,5,8,…

import java.util.Scanner;

public class Recursion {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();

        System.out.println(fun(n));
    }

    public static int fun(int n) {

        if (n <= 2) {
            return 1;
        }
        else {
            return fun(n-1) + fun(n-2);
        }
    }
}

4、二叉树的遍历(前、中、后)

此代码由Java架构师必看网-架构君整理
import java.util.Arrays; import java.util.LinkedList; public class MyBinaryTree { //二叉树节点 private static class TreeNode{ int data; TreeNode leftChild; TreeNode rightChile; public TreeNode(int data) { this.data = data; } } //构建二叉树 public static TreeNode createBinaryTree(LinkedList<Integer> inputList) { TreeNode node = null; if(inputList == null || inputList.isEmpty()) { return null; } Integer data = inputList.removeFirst(); //如果元素为空,则不再递归 if(data != null){ node = new TreeNode(data); node.leftChild = createBinaryTree(inputList); node.rightChile = createBinaryTree(inputList); } return node; } //前序遍历:根节点,左子树,右子树 public static void preOrderTraveral(TreeNode node) { if (node == null) { return; } System.out.println(node.data); preOrderTraveral(node.leftChild); preOrderTraveral(node.rightChile); } //中序遍历:左子树,根节点,右子树 public static void inOrderTraveral(TreeNode node) { if(node == null) { return; } inOrderTraveral(node.leftChild); System.out.println(node); inOrderTraveral(node.rightChile); } //后序遍历:左子树,右子树,根节点 public static void postOrderTraveral(TreeNode node) { if (node == null) { return; } postOrderTraveral(node.leftChild); postOrderTraveral(node.rightChile); System.out.println(node.data); } public static void main(String[] args) { LinkedList<Integer> inputList = new LinkedList<Integer>(Arrays.asList(new Integer[]{3,2,9,null,null,10,null,null,8,null,4})); TreeNode treeNode = createBinaryTree(inputList); System.out.println("前序遍历:"); preOrderTraveral(treeNode); System.out.println("中序遍历:"); inOrderTraveral(treeNode); System.out.println("后序遍历:"); postOrderTraveral(treeNode); } }

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