二叉树的最小深度

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