leetcode--Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

public class Solution {
    public int minDepth(TreeNode root) {
       int depth = 0;
	   if(root != null){
	        if(root.left == null)
			    depth = 1 + minDepth(root.right);
			else if(root.right == null)
			    depth = 1 + minDepth(root.left);
			else
			    depth = 1 + Math.min(minDepth(root.left), minDepth(root.right));
	   } 
		return depth;
    }
}