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 Your Coffee".

Return the modified string after the spaces have been added.

https://leetcode.com/problems/adding-spaces-to-a-string/

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.

#Test Cases

class Solution:
    def addSpaces(self, s: str, spaces: List[int]) -> str:

import pytest

from solution import Solution


@pytest.mark.parametrize('s, spaces, expected', [
    ("LeetcodeHelpsMeLearn", [8,13,15], "Leetcode Helps Me Learn"),
    ("icodeinpython", [1,5,7,9], "i code in py thon"),
    ("spacing", [0,1,2,3,4,5,6], " s p a c i n g"),
])
class Test:
    def test_solution(self, s, spaces, expected):
        sol = Solution()
        assert sol.addSpaces(s, spaces) == expected

#Thoughts

#Code

class Solution:
    def addSpaces(self, s: str, spaces: list[int]) -> str:
        def ranges():
            prev = 0
            for val in spaces:
                yield prev, val
                prev = val

            yield spaces[-1], len(s)

        return ' '.join(s[b:e] for b, e in ranges())