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Java-based LeetCode algorithm problem solutions, regularly updated

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package g2101_2200.s2109_adding_spaces_to_a_string;

// #Medium #Array #String #Simulation #2022_05_31_Time_24_ms_(89.33%)_Space_94.5_MB_(48.03%)

/**
 * 2109 - Adding Spaces to a String\.
 *
 * Medium
 *
 * 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 "Leetcode**H**elps**M**e**L**earn". 
 *
 * 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 "i**c**ode**i**n**p**y**t**hon". 
 *
 * 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**.
**/
public 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);
    }
}