606. Construct String from Binary Tree-优快云博客

本文介绍了一种将二叉树转换为字符串的算法，并提供C++和Java两种实现方式。该算法通过先序遍历的方式构造由括号和整数组成的字符串，空节点用空括号对表示，同时省略不影响一对一映射关系的空括号对。

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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.

/*C++ Solution*/
/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int travelTree(TreeNode * t,string & str) {
        if(t == NULL){
            return -1;
        }

        str.append(to_string(t->val));
        if(t->left){
            str.append("(");
            travelTree(t->left,str);
            str.append(")");
        }

        if(t->right){
            if(!t->left){
               str.append("()");
            }
            str.append("(");
            travelTree(t->right,str);
            str.append(")");
        }

        return 0;
    }

    string tree2str(TreeNode* t) {
        string str;
        travelTree(t,str);

        return str;
    }
};

/*java solution*/
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public String str = new String();
    public boolean travelTree(TreeNode t) {
        if(t == null){
            return false;
        }

        str += Integer.toString(t.val);
        if(t.left!=null){
            str += "(";
            travelTree(t.left);
            str += ")";
        }

         if(t.right!=null){
             if(t.left == null){
                str += "()";
             }
            str += "(";
            travelTree(t.right);
            str += ")";
        }

        return true;
    }
    public String tree2str(TreeNode t) {
       travelTree(t);
       return str;
    }
}