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.

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int minDepth(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(root == null){
            return 0;
        }
        int left = 0, right = 0;
        if(root.left != null){
            left = minDepth(root.left);
        }
        
        if(root.right != null){
            right = minDepth(root.right);
        }
        
        if(root.left != null && root.right != null)
            return 1 + Math.min(left, right);
        else if(root.left == null && root.right != null){
            return 1 + right;
        } else if(root.left != null && root.right == null){
            return 1 + left;
        } else {
            return 1;
        }
        
    }
}