zoukankan      html  css  js  c++  java
  • 606. Construct String from Binary Tree

    You need to construct a string consists of parenthesis and integers from a binary tree with the preorder traversing way.

    The null node needs to be represented by empty parenthesis pair "()". And you need to omit all the empty parenthesis pairs that don't affect the one-to-one mapping relationship between the string and the original binary tree.

    Example 1:

    Input: Binary tree: [1,2,3,4]
           1
         /   
        2     3
       /    
      4     
    
    Output: "1(2(4))(3)"
    
    Explanation: Originallay it needs to be "1(2(4)())(3()())",
    but you need to omit all the unnecessary empty parenthesis pairs.
    And it will be "1(2(4))(3)".

    Example 2:

    Input: Binary tree: [1,2,3,null,4]
           1
         /   
        2     3
           
          4 
    
    Output: "1(2()(4))(3)"
    
    Explanation: Almost the same as the first example,
    except we can't omit the first parenthesis pair to break the one-to-one mapping relationship between the input and the output.

    分4种情况考虑:

    1. 左右子节点都没有,不加()

    2. 左右子节点都有,不加()

    3. 只有左子节点,不加()

    4. 只有右子节点,加()

    time: O(n), space: O(height)

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    class Solution {
        public String tree2str(TreeNode t) {
            if(t == null) {
                return "";
            }
            if(t.left == null && t.right == null) {
                return Integer.toString(t.val);
            }
            if(t.right == null) {
                return t.val + "(" + tree2str(t.left) + ")" + tree2str(t.right);
            }
            return t.val + "(" + tree2str(t.left) + ")" + "(" + tree2str(t.right) + ")";
        }
    }
  • 相关阅读:
    2018-2019-2 实验三 敏捷开发与XP实践
    计算机网络课外实验一级 20175319江野
    2018-2019-2 《Java程序设计》第9周学习总结
    MyCP(课下作业,必做)
    [NOIP2012] 疫情控制
    [SPOJ2021] Moving Pebbles
    谁能赢呢?
    [HEOI2014] 人人尽说江南好
    [笔记] 巴什博弈
    [SCOI2008] 着色方案
  • 原文地址:https://www.cnblogs.com/fatttcat/p/10198671.html
Copyright © 2011-2022 走看看