leetcode226. 翻转二叉树

leetcode226. 翻转二叉树

题目描述

链接: leetcode226.

翻转一棵二叉树。

示例：
输入

输出

题解

public class leetcode226 {
    public class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;

        TreeNode() {}

        TreeNode(int val) {
            this.val = val;
        }

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

    public TreeNode invertTreeIteratively(TreeNode root) {
        if (root == null) {
            return null;
        }
        TreeNode newTree = new TreeNode(root.val);
        newTree.left = invertTree(root.right);
        newTree.right = invertTree(root.left);
        return newTree;
    }

    public TreeNode invertTreeRecursively(TreeNode root) {
        if (root == null) {
            return null;
        }
        LinkedList<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(!queue.isEmpty()) {
            TreeNode node = queue.poll();
            exchangeTreeNode(node);
            if (node.left != null) {
                queue.add(node.left);
            }
            if (node.right != null) {
                queue.add(node.right);
            }
        }
        return root;
    }

    private void exchangeTreeNode(TreeNode node) {
        TreeNode left = node.left;
        node.left = node.right;
        node.right = left;
    }
}