Minimum Depth of Binary Tree

/*
 * time complexity is O(n), because every node visit once, is it right?
 */
public class Minimum_depth_of_binary_tree {
 
 public class TreeNode {
     int val;
     TreeNode left;
     TreeNode right;
     TreeNode(int x) { val = x; }
 }
 public int minDepth(TreeNode root) {
  //shortest path form the root node down to the nearest leaf node
  if (root == null) {return 0;}

  return getMin(root);
    }
 
 public int getMin(TreeNode root) {
  if (root == null) {
   return Integer.MAX_VALUE;
  }
  if (root.right == null && root.left == null) {
   return 1;
  }
  return Math.min(getMin(root.left), getMin(root.right)) + 1;
 }
}