1663. Smallest String With A Given Numeric Value

package LeetCode_1663

/**
 * 1663. Smallest String With A Given Numeric Value
 * https://leetcode.com/problems/smallest-string-with-a-given-numeric-value/
 *
 * The numeric value of a lowercase character is defined as its position (1-indexed) in the alphabet,
 * so the numeric value of a is 1, the numeric value of b is 2, the numeric value of c is 3, and so on.
The numeric value of a string consisting of lowercase characters is defined as the sum of its characters' numeric values.
For example, the numeric value of the string "abe" is equal to 1 + 2 + 5 = 8.
You are given two integers n and k. Return the lexicographically smallest string with length equal to n and numeric value equal to k.
Note that a string x is lexicographically smaller than string y if x comes before y in dictionary order, that is, either x is a prefix of y,
or if i is the first position such that x[i] != y[i], then x[i] comes before y[i] in alphabetic order.

Example 1:
Input: n = 3, k = 27
Output: "aay"
Explanation: The numeric value of the string is 1 + 1 + 25 = 27, and it is the smallest string with such a value and length equal to 3.

Example 2:
Input: n = 5, k = 73
Output: "aaszz"

Constraints:
1. 1 <= n <= 105
2. n <= k <= 26 * n
 * */
class Solution {
    /*
    * solution: Greedy, fill in reverse order, Time:O(k), Space:O(n)
    * */
    fun getSmallestString(n: Int, k_: Int): String {
        var k = k_
        val chars = CharArray(n) { 'a' }
        //because filled n 'a', so reduce k by n
        k -= n
        var i = n - 1
        //replace by 'a'+25 or 'a'+k
        while (k > 0) {
            val closestOne = Math.min(25, k)
            chars[i] = chars[i] + closestOne
            k -= closestOne
            i--
        }
        return String(chars)
    }
}