/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int minDepth(TreeNode root) {
        if (root == null){
            return 0;
        } else if(root.left == null) {
            return minDepth(root.right) + 1;
        } else if(root.right == null) {
            return minDepth(root.left) + 1;
        }
        return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
    }
}


/*
[]
[1]
[1,1]
[1,null,2]
[1,2,3,null,null,1,2,1,null,null,null,1]
*/