/**
 * You are given two strings word1 and word2.
 * Merge the strings by adding letters in alternating order, starting with word1.
 * If a string is longer than the other, append the additional letters onto the end of the merged string.
 *
 * Return the merged string.
 *
 *
 *
 * Example 1:
 *
 * Input: word1 = "abc", word2 = "pqr"
 * Output: "apbqcr"
 * Explanation: The merged string will be merged as so:
 * word1:  a   b   c
 * word2:    p   q   r
 * merged: a p b q c r
 * Example 2:
 *
 * Input: word1 = "ab", word2 = "pqrs"
 * Output: "apbqrs"
 * Explanation: Notice that as word2 is longer, "rs" is appended to the end.
 * word1:  a   b
 * word2:    p   q   r   s
 * merged: a p b q   r   s
 * Example 3:
 *
 * Input: word1 = "abcd", word2 = "pq"
 * Output: "apbqcd"
 * Explanation: Notice that as word1 is longer, "cd" is appended to the end.
 * word1:  a   b   c   d
 * word2:    p   q
 * merged: a p b q c   d
 *
 *
 * Constraints:
 *
 * 1 <= word1.length, word2.length <= 100
 * word1 and word2 consist of lowercase English letters.
 * @see <a href="https://leetcode.com/problems/merge-strings-alternately/">LeetCode</a>
 */
fun mergeAlternately(word1: String, word2: String): String {
    var word1Index = 0
    var word2Index = 0
    return buildString {
        for (index in 0 until word1.length + word2.length) {
            if (word1Index < word1.length && (index.rem(2) == 0 || word2Index >= word2.length)) {
                append(word1[word1Index])
                word1Index++
            } else {
                append(word2[word2Index])
                word2Index++
            }
        }
    }
}
