606. Construct String from Binary Tree

最新推荐文章于 2021-02-16 03:26:06 发布

原创最新推荐文章于 2021-02-16 03:26:06 发布 · 182 阅读

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#Tree

本文介绍了一种将二叉树以先序遍历的方式转换为由括号和整数组成的字符串的方法。空节点用()表示，并省略不影响唯一性的多余空括号对。通过两个实例演示了算法的应用过程。

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.

class Solution {
public:
    string tree2str(TreeNode* t) {
        if(!t) return "";
        string str = to_string(t->val);
        if(t->left)
        {
            str+="(";
            str+=tree2str(t->left);
            str+=")";
        }
        if(t->right)
        {
            if(t->left==NULL)
                str+="()";
            str+="(";
            str+=tree2str(t->right);
            str+=")";
        }
        return str;
    }
};