二叉树的先根、中根、后根的递归与非递归调用方法，全！精简版代码！

Myth丶恋晨 2022-04-02 06:45 160阅读 0赞

整理了一下这几种遍历的精简版代码，思路简介明确，其中后序非递归方法用到了双栈，代码如下：

import LinkedStack;
    import BinaryNode;
    import org.junit.Test;
    
    public class PosIterator<T> {
        private BinaryNode root;
    
        //递归的算法   ---先根遍历
        public void preRead(BinaryNode<Integer> p) {
            if (p != null) {
                System.out.println(p.data);
                preRead(p.left);
                preRead(p.right);
            }
        }
    
        //递归的算法   ---中根遍历
        public void inRead(BinaryNode<Integer> p) {
            if (p != null) {
                inRead(p.left);
                System.out.println(p.data);
                inRead(p.right);
            }
        }
    
        //递归的算法   ---后根遍历
        public void posRead(BinaryNode<Integer> p) {
            if (p != null) {
                posRead(p.left);
                posRead(p.right);
                System.out.println(p.data);
            }
        }
    
        //非递归算法   ---先根遍历
        public void preOrderTraverse() {
            System.out.println("根遍历（非递归）：   ");
            LinkedStack<BinaryNode<T>> stack = new LinkedStack<BinaryNode<T>>();
            BinaryNode<T> p = this.root;
            while (p != null || !stack.isEmpty()) {
                if (p != null) {
                    stack.push(p);
                    p = p.left;
                }
                else {
                    System.out.print("^");
                    p = stack.pop();
                    System.out.print(p.data);//访问数据。
                    p = p.right;
                }
            }
            System.out.println();
        }
    
        //非递归算法   ---中根遍历
        public void inOrderTraverse() {
            System.out.println("中根遍历（非递归）：   ");
            LinkedStack<BinaryNode<T>> stack = new LinkedStack<BinaryNode<T>>();
            BinaryNode<T> p = this.root;
            while (p != null || !stack.isEmpty()) {
                if (p != null) {
                    System.out.print(p.data);//访问数据。
                    stack.push(p);
                    p = p.left;
                }
                else {
                    System.out.print("^");
                    p = stack.pop();
                    p = p.right;
                }
            }
            System.out.println();
        }
    
        //非递归算法   ---后根遍历  --双栈
        public void posOrderTraverse(BinaryNode<T> root) {
            System.out.println("后根遍历（非递归）：   ");
            LinkedStack<BinaryNode<T>> stack1 = new LinkedStack<BinaryNode<T>>(); //创建立空栈1
            LinkedStack<BinaryNode<T>> stack2 = new LinkedStack<BinaryNode<T>>(); //创建立空栈1
            stack1.push(root);
             while (!stack1.isEmpty()) {
                 BinaryNode<T> p = stack1.pop();
                 stack2.push(p);
                 if (p.right != null) {
                     stack1.push(p.right);
                 }
                 if (p.left != null) {
                     stack1.push(p.left);
                 }
             }
    
             while (!stack2.isEmpty()) {
                 System.out.print(stack2.pop().data);
             }
             System.out.println();
        }
    
        @Test
        public void testIt() {
            this.root = new BinaryNode<String>("A");
            this.root.left = new BinaryNode("B");
            this.root.left.left = new BinaryNode("D");
            this.root.left.left.right = new BinaryNode("G");
            this.root.right = new BinaryNode("C");
            this.root.right.left = new BinaryNode("E");
            this.root.right.right = new BinaryNode("F");
            this.root.right.right.left = new BinaryNode("H");
    
            this.posOrderTraverse(this.root);
            this.inOrderTraverse();
            this.preOrderTraverse();
        }
    
    }

附赠引用到的两个类的代码：

public class BinaryNode<T> {
        public T data;
        public BinaryNode<T> left, right;
    
        public BinaryNode(T data, BinaryNode<T> left, BinaryNode<T> right) {
            this.data = data;
            this.left = left;
            this.right = right;
        }
    
        public BinaryNode(T data) {
            this(data,null,null);
        }
    
        public String toString() {
            return this.data.toString();
        }
    
        public boolean isLeaf() {
            return this.left == null && this.right == null;
        }
    }

package dataDistructure;
    
    import java.util.LinkedList;
    import java.util.List;
    
    public class LinkedStack<T> {
        private List<T> list;
    
        public LinkedStack() {
            this.list = new LinkedList<T>();
        }
    
        public boolean isEmpty() {
            return this.list.isEmpty();
        }
    
        public void push(T t) {
            this.list.add(t);
        }
    
        public T peek() {
            return this.list.get(this.list.size()-1);
        }
    
        public T pop() {
            T t = this.list.get(this.list.size()-1);
            this.list.remove(this.list.size()-1);
            return t;
        }
    }