110. 平衡二叉树

原题

https://leetcode.cn/problems/balanced-binary-tree/description/

思路

2个递归, 求每个节点的深度和判断每个节点是否为平衡二叉树

复杂度

时间：O(n)
空间：O(n)

Python代码

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isBalanced(self, root: Optional[TreeNode]) -> bool:
        def depth(root):
            if not root:
                return 0
            return 1 + max(depth(root.left), depth(root.right))

        if not root:
            return True
        return (
            abs(depth(root.left) - depth(root.right)) <= 1
            and self.isBalanced(root.left)
            and self.isBalanced(root.right)
        )

Go代码

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func depth(root *TreeNode) int {
	if root == nil {
		return 0
	}
	return 1 + max(depth(root.Left), depth(root.Right))
}
func isBalanced(root *TreeNode) bool {
	if root == nil {
		return true
	}
	return math.Abs(float64(depth(root.Left)-depth(root.Right))) <= 1 &&
		isBalanced(root.Left) && isBalanced(root.Right)
}