Watch 10 video solutions for Smallest K-Length Subsequence With Occurrences of a Letter, a hard level problem involving String, Stack, Greedy. This walkthrough by NeetCode has 657,697 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
You are given a string s, an integer k, a letter letter, and an integer repetition.
Return the lexicographically smallest subsequence of s of length k that has the letter letter appear at least repetition times. The test cases are generated so that the letter appears in s at least repetition times.
A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.
A string a is lexicographically smaller than a string b if in the first position where a and b differ, string a has a letter that appears earlier in the alphabet than the corresponding letter in b.
Example 1:
Input: s = "leet", k = 3, letter = "e", repetition = 1 Output: "eet" Explanation: There are four subsequences of length 3 that have the letter 'e' appear at least 1 time: - "lee" (from "leet") - "let" (from "leet") - "let" (from "leet") - "eet" (from "leet") The lexicographically smallest subsequence among them is "eet".
Example 2:
Input: s = "leetcode", k = 4, letter = "e", repetition = 2 Output: "ecde" Explanation: "ecde" is the lexicographically smallest subsequence of length 4 that has the letter "e" appear at least 2 times.
Example 3:
Input: s = "bb", k = 2, letter = "b", repetition = 2 Output: "bb" Explanation: "bb" is the only subsequence of length 2 that has the letter "b" appear at least 2 times.
Constraints:
1 <= repetition <= k <= s.length <= 5 * 104s consists of lowercase English letters.letter is a lowercase English letter, and appears in s at least repetition times.