二叉树的先序、中序、后序递归和非递归遍历

绝地灬酷狼 2022-05-15 02:43 182阅读 0赞

# 二叉树遍历总结 #

import java.util.Stack;
    /** * 二叉树的遍历 * @author superman * */
    public class Code_01_PreInPosTraversal {
    
        public static class Node {
            public int value;
            public Node left;
            public Node right;
    
            public Node(int data) {
                this.value = data;
            }
        }
       //先序遍历(递归)
        public static void preOrderRecur(Node head) {
            if (head == null) {
                return;
            }
            System.out.print(head.value + " ");
            preOrderRecur(head.left);
            preOrderRecur(head.right);
        }
       //中序遍历(递归)
        public static void inOrderRecur(Node head) {
            if (head == null) {
                return;
            }
            inOrderRecur(head.left);
            System.out.print(head.value + " ");
            inOrderRecur(head.right);
        }
       //后序遍历(递归)
        public static void posOrderRecur(Node head) {
            if (head == null) {
                return;
            }
            posOrderRecur(head.left);
            posOrderRecur(head.right);
            System.out.print(head.value + " ");
        }
    
        //先序遍历(非递归)
        public static void preOrderUnRecur(Node head) {
            System.out.print("pre-order: ");
            if (head != null) {
                Stack<Node> stack = new Stack<Node>();
                stack.add(head);
                while (!stack.isEmpty()) {
                    head = stack.pop();
                    System.out.print(head.value + " ");
                    if (head.right != null) {
                        stack.push(head.right);
                    }
                    if (head.left != null) {
                        stack.push(head.left);
                    }
                }
            }
            System.out.println();
        }
       //中序遍历(非递归)
        public static void inOrderUnRecur(Node head) {
            System.out.print("in-order: ");
            if (head != null) {
                Stack<Node> stack = new Stack<Node>();
                while (!stack.isEmpty() || head != null) {
                    if (head != null) {
                        stack.push(head);
                        head = head.left;
                    } else {
                        head = stack.pop();
                        System.out.print(head.value + " ");
                        head = head.right;
                    }
                }
            }
            System.out.println();
        }
         //后序遍历(非递归)
        public static void posOrderUnRecur1(Node head) {
            System.out.print("pos-order: ");
            if (head != null) {
                Stack<Node> s1 = new Stack<Node>();
                Stack<Node> s2 = new Stack<Node>();
                s1.push(head);
                while (!s1.isEmpty()) {
                    head = s1.pop();
                    s2.push(head);
                    if (head.left != null) {
                        s1.push(head.left);
                    }
                    if (head.right != null) {
                        s1.push(head.right);
                    }
                }
                while (!s2.isEmpty()) {
                    System.out.print(s2.pop().value + " ");
                }
            }
            System.out.println();
        }
    
        public static void posOrderUnRecur2(Node h) {
            System.out.print("pos-order: ");
            if (h != null) {
                Stack<Node> stack = new Stack<Node>();
                stack.push(h);
                Node c = null;
                while (!stack.isEmpty()) {
                    c = stack.peek();
                    if (c.left != null && h != c.left && h != c.right) {
                        stack.push(c.left);
                    } else if (c.right != null && h != c.right) {
                        stack.push(c.right);
                    } else {
                        System.out.print(stack.pop().value + " ");
                        h = c;
                    }
                }
            }
            System.out.println();
        }
    
        public static void main(String[] args) {
            Node head = new Node(5);
            head.left = new Node(3);
            head.right = new Node(8);
            head.left.left = new Node(2);
            head.left.right = new Node(4);
            head.left.left.left = new Node(1);
            head.right.left = new Node(7);
            head.right.left.left = new Node(6);
            head.right.right = new Node(10);
            head.right.right.left = new Node(9);
            head.right.right.right = new Node(11);
    
            // recursive
            System.out.println("==============recursive==============");
            System.out.print("pre-order: ");
            preOrderRecur(head);
            System.out.println();
            System.out.print("in-order: ");
            inOrderRecur(head);
            System.out.println();
            System.out.print("pos-order: ");
            posOrderRecur(head);
            System.out.println();
    
            // unrecursive
            System.out.println("============unrecursive=============");
            preOrderUnRecur(head);
            inOrderUnRecur(head);
            posOrderUnRecur1(head);
            posOrderUnRecur2(head);
    
        }
    
    }

![这里写图片描述][70]

[70]: /images/20220515/22ef6372de2e49c48c8925421b45ec70.png