给予一颗二叉树,返回其每层节点的平均值.
例 :
给予树:
4
/ \
2 7
/ \ / \
1 3 6 9
返回:
4
/ \
7 2
/ \ / \
9 6 3 1
采用深度优先遍历, 从最底层节点开始, 将每个节点的左右节点进行交换即可.
/**
* 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 left = root.left;
TreeNode right = root.right;
if (left != null) {
invertTree(left);
}
if (right != null) {
invertTree(right);
}
root.left = right;
root.right = left;
return root;
}
}
Runtime: 0 ms, faster than 100.00% of Java online submissions for Invert Binary Tree. Memory Usage: 33.5 MB, less than 98.89% of Java online submissions for Invert Binary Tree.