1663. 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 <= n <= 105
• n <= k <= 26 * n

    public String getSmallestString(int n, int k) {
        char[] ca = new char[n];
        Arrays.fill(ca, 'a');
        k -= n; // Guarantee each character value is at least 1.
        for (int i = n - 1; i >= 0 && k > 0; --i) {
            ca[i] += Math.min(25, k);
            k -= Math.min(k, 25);
        }
        return String.valueOf(ca);
    }

要lexical minimum，可以先建一个长度为n的char array，fill 'a', 然后从尾部开始往头部更新，从大到小安排。

很好很强大。

https://leetcode.com/problems/smallest-string-with-a-given-numeric-value/discuss/944594/JavaPython-3-O(n)-and-O(1)-codes-w-brief-explanation-and-analysis.