递归三要素:
明确递归终止条件;
给出递归终止时的处理办法;
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);
}
}
}
2、1 * 2 * 3 * … * n
(推荐学习:java视频教程)
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)
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 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 inputList = new LinkedList(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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