110. Balanced Binary Tree

Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the left and right subtrees of every node differ in height by no more than 1.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: true

Example 2:

Input: root = [1,2,2,3,3,null,null,4,4]
Output: false

Example 3:

Input: root = []
Output: true

Constraints:

• The number of nodes in the tree is in the range [0, 5000].
• -104 <= Node.val <= 104

# @lc code=start
using LeetCode

is_balanced_binary_tree(::Nothing) = true
function is_balanced_binary_tree(root::TreeNode)::Bool
    tree_depth(::Nothing, depth::Int) = depth
    function tree_depth(tree::TreeNode, depth::Int)::Int
        # -1 for if tree is not balanceed
        (lt = tree_depth(tree.left, depth + 1)) == -1 && return -1
        (rt = tree_depth(tree.right, depth + 1)) == -1 && return -1
        return abs(lt - rt) <= 1 ? max(lt, rt) : -1
    end
    return tree_depth(root, 0) != -1
end
# @lc code=end

is_balanced_binary_tree (generic function with 2 methods)

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