1754. Largest Merge Of Two Strings

package LeetCode_1754

/**
 * 1754. Largest Merge Of Two Strings
 * https://leetcode.com/problems/largest-merge-of-two-strings/
 * You are given two strings word1 and word2. You want to construct a string merge in the following way:
 * while either word1 or word2 are non-empty, choose one of the following options:
If word1 is non-empty, append the first character in word1 to merge and delete it from word1.
For example, if word1 = "abc" and merge = "dv", then after choosing this operation, word1 = "bc" and merge = "dva".
If word2 is non-empty, append the first character in word2 to merge and delete it from word2.
For example, if word2 = "abc" and merge = "", then after choosing this operation, word2 = "bc" and merge = "a".
Return the lexicographically largest merge you can construct.
A string a is lexicographically larger than a string b (of the same length) if in the first position where a and b differ,
a has a character strictly larger than the corresponding character in b.
For example, "abcd" is lexicographically larger than "abcc" because the first position they differ is at the fourth character,
and d is greater than c.

Example 1:
Input: word1 = "cabaa", word2 = "bcaaa"
Output: "cbcabaaaaa"
Explanation: One way to get the lexicographically largest merge is:
- Take from word1: merge = "c", word1 = "abaa", word2 = "bcaaa"
- Take from word2: merge = "cb", word1 = "abaa", word2 = "caaa"
- Take from word2: merge = "cbc", word1 = "abaa", word2 = "aaa"
- Take from word1: merge = "cbca", word1 = "baa", word2 = "aaa"
- Take from word1: merge = "cbcab", word1 = "aa", word2 = "aaa"
- Append the remaining 5 a's from word1 and word2 at the end of merge.
 * */
class Solution {
    /*
    * solution: merge and compare,
    * Time:O(l*max(word1.length,word2.length)), Space:O(l), l = word1.length + word2.length
    * */
    fun largestMerge(word1: String, word2: String): String {
        val sb = StringBuilder()
        var i = 0
        var j = 0
        while (i < word1.length && j < word2.length) {
            /*
            * if current two chars are equals, compare remaining string after current char
            * */
            if (word1[i] > word2[j] || (word1[i] == word2[j] && word1.substring(i).compareTo(word2.substring(j)) > 0)) {
                sb.append(word1[i++])
            } else {
                sb.append(word2[j++])
            }
        }
        while (i < word1.length) {
            sb.append(word1[i++])
        }
        while (j < word2.length) {
            sb.append(word2[j++])
        }
        return sb.toString()
    }
}