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Minimum Depth of Binary Tree

Problem statement​

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

Note: A leaf is a node with no children.

Example 1:

Input: root = [3,9,20,null,null,15,7]Output: 2

Example 2:

Input: root = [2,null,3,null,4,null,5,null,6]Output: 5

Constraints:

  • The number of nodes in the tree is in the range [0, 105].
  • -1000 <= Node.val <= 1000

My solution​

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number}
 */
var minDepth = function(root) {
    if (!root) {
        return 0
    }
    let result;
    
    function dfs(node, height) {
        if (!node.left && !node.right) {
            result = Math.min(result || height, height)
        }
        
        if (node.left) {
            dfs(node.left, height + 1)
        }
        
        if (node.right) {
            dfs(node.right, height + 1)
        }
    }
    
    dfs(root, 1)
    return result;
};