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.