LeetCode解题报告（281）-- 1663. Smallest String With A Given Numeric Value

Problem

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:

1
2
3

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:

1 2	Input: n = 5, k = 73 Output: "aaszz"

Constraints:

1 <= n <= 105
n <= k <= 26 * n

Analysis

题目给了两个数字，n是长度，k是总和。求出长度为n，总和为k的且字典序最小的字符串。因为要的是字典序最小的，这里直接用贪心就好了，不过要注意顺序是从后往前。原因是从前往后的话，先选小的后面可能无法凑够总和，但是从后往前的话，先选大的话，前面一定能凑好。

Solution

因为长度n是确定的，都初始化为最小的a，然后，这样余额就变成了k - n ，然后从后往前，如果余额比25大，直接选最大的z，循环结束后的result就是答案。

Code

class Solution {
public:
    string getSmallestString(int n, int k) {
        k -= n;
        string result(n, 'a');
        
        for (int i = n - 1; i >= 0; i--) {
            int d = min(k, 25);
            result[i] += d;
            k -= d;
        }
        return result;
    }
};

Summary

这道题目是贪心算法的一个简单应用，难度不大，主要是初始化讲究一点技巧。这道题这道题目的分享到这里，谢谢您的支持！