1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     
12     public int minDepth(TreeNode root) {
13         
14         Stack<Integer> stack=new Stack<>();
15         int depth=0;
16        if(root==null)
17        return 0;
18        
19        if(root.left==null&&root.right==null)
20        {return 1;}
21        
22        if(root.left!=null)
23        {
24            depth=1+minDepth(root.left);
25 26            if(stack.empty()||stack.peek()>depth)
27            stack.push(depth);
28        }
29        
30        
31         if(root.right!=null)
32        {
33            depth=1+minDepth(root.right);
34             if(stack.empty()||stack.peek()>depth)
35             stack.push(depth);
36        }
37       
38        return stack.peek();
39     }
40 }