【leetcode】1663. Smallest String With A Given Numeric Value

题目如下：

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

解题思路：贪心算法， 每一位先用a尝试，如果剩余部分全部用z的话所组成的和扔小于k，接下来尝试b，c....只能找出满足条件的值为止。

代码如下：

class Solution(object):
    def getSmallestString(self, n, k):
        """
        :type n: int
        :type k: int
        :rtype: str
        """
        res = ''
        alphabet = [''] + [chr(i) for i in range(97,123)]
        while n > 0:
            if (n - 1) * 26 >= k:
                res += 'a'
                k -= 1
            else:
                val = k - (n - 1) * 26
                res += alphabet[val]
                k -= val
            n -= 1
        return res