111. 二叉树的最小深度

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int minDepth(TreeNode root) {
        if(root == null) return 0;
        int l = minDepth(root.left);
        int h = minDepth(root.right);
        //若至少有1个为空
        if(root.left == null || root.right == null){
            return l + h + 1;
        }
        return Math.min(l,h) + 1;
    }
}