LeetCode 226. 翻转二叉树

题目描述

思路：

直接交换两个整棵子树的位置

bfs

class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) return null;
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll();
            // 交换node左右节点
            TreeNode tmp = node.left;
            node.left = node.right;
            node.right = tmp;
            if (node.left != null) {
                queue.offer(node.left);
            }
            if (node.right != null) {
                queue.offer(node.right);
            }
        }
        return root;
    }
}

dfs

class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return root;
        }
        TreeNode tmp = root.left;
        root.left = invertTree(root.right);
        root.right = invertTree(tmp);
        return root;
    }
}


class Solution {
    public TreeNode invertTree(TreeNode root) {
        invert(root);
        return root;
    }
    public void invert(TreeNode root) {
        if (root == null) {
            return;
        }
        // swap
        TreeNode tmp = root.left;
        root.left = root.right;
        root.right = tmp;
        //对子树操作
        invertTree(root.left);
        invertTree(root.right);
    }
}

//合在一起写法
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }
        TreeNode tmp = root.left;
        root.left = root.right;
        root.right = tmp;
        invertTree(root.left);
        invertTree(root.right);
        return root;
    }
}