二叉树的先序，中序，后序递归和非递归实现

来源：互联网发布：休闲食品数据编辑：程序博客网时间：2024/05/17 22:23

二叉树l结构类定义：

public class TreeNode { int val ;TreeNode left ;TreeNode right ;public TreeNode(int val){this.val = val ;left = null ;right = null ;}}

测试二叉树：
1
2 3
4 5 6 7
8 10
9
先序遍历

public class PreOrder {//递归方法public  static void preorder1(TreeNode root){if(root == null) return ;System.out.print(root.val + " ");if(root.left!=null) preorder1(root.left);if(root.right != null) preorder1(root.right);}//非递归方法public static void preorder2(TreeNode root){LinkedList<TreeNode> stack = new LinkedList<TreeNode>();if(root ==  null) return ;TreeNode p = root ;stack.push(p);while(!stack.isEmpty()){TreeNode temp = stack.pop();System.out.print(temp.val + " ");if(temp.right != null) stack.push(temp.right);if(temp.left != null) stack.push(temp.left);}}public static void main(String[] args){TreeNode root = GeneratorTree.getTree();System.out.print("递归先序遍历：");preorder1(root);System.out.println();System.out.print("非递归先序遍历：");preorder2(root);}}

输出：
递归先序遍历：1 2 4 8 9 10 5 3 6 7
非递归先序遍历：1 2 4 8 9 10 5 3 6 7

中序遍历：

public class InOrder {//递归遍历public  static void inorder1(TreeNode root){if(root == null) return ;if(root.left!=null) inorder1(root.left);System.out.print(root.val + " ");if(root.right != null) inorder1(root.right);}//非递归遍历public static void inorder2(TreeNode root){LinkedList<TreeNode> stack = new LinkedList<TreeNode>();if(root == null ) return ;TreeNode p = root ; ;while(p != null || !stack.isEmpty()){if(p != null){stack.push(p);p = p.left;}else{p = stack.pop();System.out.print(p.val + " ");p = p.right ;}}}public static void main(String[] args){TreeNode root = GeneratorTree.getTree();System.out.print("递归中序遍历：");inorder1(root);System.out.println();System.out.print("非递归中序遍历：");inorder2(root);}}

输出：
递归中序遍历：8 9 4 10 2 5 1 6 3 7
非递归中序遍历：8 9 4 10 2 5 1 6 3 7

后序遍历：

public class PostOrder {//递归遍历public  static void postorder1(TreeNode root){if(root == null) return ;if(root.left!=null) postorder1(root.left);if(root.right != null) postorder1(root.right);System.out.print(root.val + " ");}//非递归遍历public static void postorder2(TreeNode root){if(root == null) return ;TreeNode p = root ;TreeNode pre = p ;                        //记录最近出栈元素LinkedList<TreeNode> stack = new LinkedList<TreeNode>();boolean flag = true ;                      //标记变量，表示当前是继续入栈还是出栈while( p!= null || !stack.isEmpty()){if(p!=null && flag == true){stack.push(p);p = p.left ;}else{if(stack.isEmpty()) return ;p = stack.peek() ;if(p.right != null && p.right != pre){p = p.right ;flag = true ;}else{p = stack.pop();System.out.print(p.val + " ");pre = p ;flag = false ;}}}}public static void main(String[] args){TreeNode root = GeneratorTree.getTree();System.out.print("递归后序遍历：");postorder1(root);System.out.println();System.out.print("非递归后序遍历：");postorder2(root);}}

输出：
递归后序遍历：9 8 10 4 5 2 6 7 3 1
非递归后序遍历：9 8 10 4 5 2 6 7 3 1

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