Minimum depth of binary tree

I was close but couldn't completely figure out dfs of binary tree.
class Solution {
    public int minDepth(TreeNode root) {
       if(root==null) return 0;
       if(root.left==null && root.right==null) return 1;
        if(root.left==null) return minDepth(root.right)+1;
        if(root.right==null) return minDepth(root.left)+1;
        //if both children present
        return Math.min(minDepth(root.left), minDepth(root.right))+1;
    }
}
#approach 2: Before reading this, my naive soul thought dfs would be the best approach since it asks you to calculate depth and not breadth. i was wrong.
  if(root!=null){
           int d=1;
            Queue<TreeNode> q=new LinkedList<>();
            q.add(root);
            while(!q.isEmpty()){
                int cnt=q.size();
                while(cnt-->0){
                    TreeNode node=q.poll();
                    if(node.left==null && node.right==null) return d;
                    if(node.left!=null) q.add(node.left);
                    if(node.right!=null) q.add(node.right);
                }
                d++;
                    
            }
        }
        return 0;
    }
    This one is more efficient, no need to traverse depth of every branch before telling the node count. kudos to the author.