[leetcode]226.Invert Binary Tree

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題目

Invert a binary tree.
比如原來的樹為 0 1 2
逆轉後的樹為 0 2 1
也就是把所有結點的左右結點互換

解法一思路

遞迴

代碼

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */class Solution {    public TreeNode invertTree(TreeNode root) {        if(root == null) return root;        TreeNode tmp = invertTree(root.right);        root.right = invertTree(root.left);        root.left = tmp;        return root;    }}

解法二思路

非遞迴，用樹的層次遍曆

代碼

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */class Solution {    public TreeNode invertTree(TreeNode root) {        if(root == null) return root;                Queue<TreeNode> queue = new LinkedList<>();        queue.offer(root);        while(!queue.isEmpty()) {            TreeNode tmp = queue.poll();            TreeNode left = tmp.left;            tmp.left = tmp.right;            tmp.right = left;                        if(tmp.left != null) queue.offer(tmp.left);            if(tmp.right != null) queue.offer(tmp.right);        }        return root;    }}

[leetcode]226.Invert Binary Tree