Today I have done leetcode's December LeetCoding Challenge with cpp.

December LeetCoding Challenge 8

Description

Construct String from Binary Tree

Given the root of a binary tree, construct a string consisting of parenthesis and integers from a binary tree with the preorder traversal way, and return it.

Omit all the empty parenthesis pairs that do not affect the one-to-one mapping relationship between the string and the original binary tree.

Example 1:

Input: root = [1,2,3,4]
Output: "1(2(4))(3)"
Explanation: Originally, 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: root = [1,2,3,null,4]
Output: "1(2()(4))(3)"
Explanation: Almost the same as the first example, except we cannot omit the first parenthesis pair to break the one-to-one mapping relationship between the input and the output.

Constraints:

• The number of nodes in the tree is in the range [1, 104].
• -1000 <= Node.val <= 1000

Solution

class Solution {
public:
  string largestOddNumber(string num) {
    int begin = 0;
    while(begin < num.length() && !(num[begin] - '0')) {
      begin += 1;
    }
    int end = begin - 1;
    for(int i = begin; i < num.length(); ++i) {
      if((num[i] - '0') & 1) {
        end = i;
      }
    }
    return num.substr(begin, end - begin + 1);
  }
};

// Accepted
// 196/196 cases passed (32 ms)
// Your runtime beats 31.44 % of cpp submissions
// Your memory usage beats 24.39 % of cpp submissions (15.4 MB)