104. Maximum Depth of Binary Tree

Python

class Solution:
    def maxDepth(self, root: Optional[TreeNode]) -> int:
        if not root:
            return 0
        return self._travel(0, root)

    def _travel(self, level, node):
        if not node:
            return level

        return max(self._travel(level+1, node.left), self._travel(level+1, node.right))

Go

func maxDepth(root *TreeNode) int {
    if root == nil {
        return 0
    }
    return travel(0, root)
}

func travel(level int, node *TreeNode) int {
    if node == nil {
        return level
    }

    leftLevel := travel(level+1, node.Left)
    rightLevel := travel(level+1, node.Right)

    if leftLevel > rightLevel {
        return leftLevel
    } else {
        return rightLevel
    }
}

Javascript

var maxDepth = function(root) {
    if (root === undefined) {
        return 0
    }

    return travel(root, 0)
};

var travel = (node, level) => {
    if (node === null) {
        return level
    }

    return Math.max(travel(node.left, level+1), travel(node.right, level+1))
}