leetcode 606. Construct String from Binary Tree | 606. 根据二叉树创建字符串

女爷i 2022-10-17 11:10 106阅读 0赞

## 题目 ##

[https://leetcode-cn.com/problems/construct-string-from-binary-tree/][https_leetcode-cn.com_problems_construct-string-from-binary-tree]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_16_color_FFFFFF_t_70]

## 题解 ##

当右子树非空时，不管有没有左子树，一定要用`()`将左子树撑起来。

其余情况就不用瞎折腾了。

/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */
    class Solution { 
        public String tree2str(TreeNode root) { 
            if (root == null) return "";
            String l = tree2str(root.left);
            String r = tree2str(root.right);
            StringBuilder sb = new StringBuilder();
            sb.append(root.val);
            if (r.length() > 0) {  // 若有右子树，则左子树一定要撑起来
                sb.append("(").append(l).append(")");
                sb.append("(").append(r).append(")");
            } else if (l.length() > 0) {  // 没有右子树且有左子树
                sb.append("(").append(l).append(")");
            }
            return sb.toString();
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_1_color_FFFFFF_t_70]

[https_leetcode-cn.com_problems_construct-string-from-binary-tree]: https://leetcode-cn.com/problems/construct-string-from-binary-tree/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_16_color_FFFFFF_t_70]: /images/20221014/89b548659d8745f98fa5ef3b54cec7b9.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NpbmF0XzQyNDgzMzQx_size_1_color_FFFFFF_t_70]: /images/20221014/940b3ee6bbd74fb2b40a40d08e21c38b.png