Minimum Depth of Binary Tree

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