Marc Lester Tan

Here’s another shot at a tree traversal problem. This solution uses Depth-First Traversal.

/**
 * Example:
 * var ti = TreeNode(5)
 * var v = ti.`val`
 * Definition for a binary tree node.
 * class TreeNode(var `val`: Int) {
 *     var left: TreeNode? = null
 *     var right: TreeNode? = null
 * }
 */
class Solution {
    var min = 0
    fun minDepth(root: TreeNode?): Int {
        if(root == null) return 0
        if(root?.left == null) return minDepth(root?.right) + 1
        if(root?.right == null) return minDepth(root?.left) + 1
        
        return Math.min(minDepth(root?.left), minDepth(root?.right)) + 1
    }
}

Runtime: 180 ms, faster than 41.67% of Kotlin online submissions for Minimum Depth of Binary Tree.
Memory Usage: 35 MB, less than 100.00% of Kotlin online submissions for Minimum Depth of Binary Tree.