1663. Smallest String With A Given Numeric Value (M)

Smallest String With A Given Numeric Value (M)

题目

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 <= 10^5
• n <= k <= 26 * n

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题意

用26个字母组成指定长度，且所有字母在字母表中出现的位次之和为指定值的字符串，使得到的串的字典序最小。

思路

贪心，从字符串的最后一个位置向前遍历，每次都尽可能的放入一个最大的字符，这样能保证前面的字符尽可能的小。第i个位置最大的字母为剩余和k减去i-1(最大不能超过26)。

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代码实现

Java

class Solution {
    public String getSmallestString(int n, int k) {
        StringBuilder sb = new StringBuilder();
        int[] arr = new int[n];
        while (n > 0 && k > 0) {
            int index = Math.min(26, k - n + 1);
            arr[--n] = index - 1;
            k -= index;
        }
        for (int i = 0; i < arr.length; i++) {
            sb.append((char) (arr[i] + 'a'));
        }
        return sb.toString();
    }
}