2109. Adding Spaces to a String

Problem

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 **Y**our **C**offee".

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 * 10^5

• s consists only of lowercase and uppercase English letters.

• 1 <= spaces.length <= 3 * 10^5

• 0 <= spaces[i] <= s.length - 1

• All the values of spaces are strictly increasing.

Solution (Java)

class Solution {
    public String addSpaces(String string, int[] spaces) {
        char[] stringChars = new char[string.length() + spaces.length];
        for (int i = 0; i < spaces.length; i++) {
            stringChars[spaces[i] + i] = ' ';
        }

        int equivalentIndex = -1;
        int i = 0;
        while (i < string.length()) {
            equivalentIndex++;
            if (stringChars[equivalentIndex] == ' ') {
                i--;
            } else {
                stringChars[equivalentIndex] = string.charAt(i);
            }
            i++;
        }
        return new String(stringChars);
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).