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

December LeetCoding Challenge 3

Description

Adding Spaces to a String

You are given a 0-indexed string s and a 0-indexed integer array spaces that describes the indices in the original string where spaces will be added. Each space should be inserted before the character at the given index.

• For example, given s = "EnjoyYourCoffee" and spaces = [5, 9], we place spaces before 'Y' and 'C', which are at indices 5 and 9 respectively. Thus, we obtain "Enjoy Your Coffee".

Return the modified string after the spaces have been added.

Example 1:

Input: s = "LeetcodeHelpsMeLearn", spaces = [8,13,15]
Output: "Leetcode Helps Me Learn"
Explanation: 
The indices 8, 13, and 15 correspond to the underlined characters in "LeetcodeHelpsMeLearn".
We then place spaces before those characters.

Example 2:

Input: s = "icodeinpython", spaces = [1,5,7,9]
Output: "i code in py thon"
Explanation:
The indices 1, 5, 7, and 9 correspond to the underlined characters in "icodeinpython".
We then place spaces before those characters.

Example 3:

Input: s = "spacing", spaces = [0,1,2,3,4,5,6]
Output: " s p a c i n g"
Explanation:
We are also able to place spaces before the first character of the string.

Constraints:

• 1 <= s.length <= 3 * 105
• s consists only of lowercase and uppercase English letters.
• 1 <= spaces.length <= 3 * 105
• 0 <= spaces[i] <= s.length - 1
• All the values of spaces are strictly increasing.

Solution

class Solution {
public:
  string addSpaces(string s, vector<int>& spaces) {
    int pos = 0;
    string answer;
    answer.reserve(s.length() + spaces.size());
    spaces.push_back(INT_MAX);
    for(int i = 0; i < s.length(); ++i) {
      if(i == spaces[pos]) {
        answer.push_back(' ');
        pos += 1;
      }
      answer.push_back(s[i]);
    }
    return answer;
  }
};

// Accepted
// 66/66 cases passed (19 ms)
// Your runtime beats 63.55 % of cpp submissions
// Your memory usage beats 89.15 % of cpp submissions (82.2 MB)