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2716. Minimize String Length
Description
Given a 0indexed string s
, repeatedly perform the following operation any number of times:
 Choose an index
i
in the string, and letc
be the character in positioni
. Delete the closest occurrence ofc
to the left ofi
(if any) and the closest occurrence ofc
to the right ofi
(if any).
Your task is to minimize the length of s
by performing the above operation any number of times.
Return an integer denoting the length of the minimized string.
Example 1:
Input: s = "aaabc" Output: 3 Explanation: In this example, s is "aaabc". We can start by selecting the character 'a' at index 1. We then remove the closest 'a' to the left of index 1, which is at index 0, and the closest 'a' to the right of index 1, which is at index 2. After this operation, the string becomes "abc". Any further operation we perform on the string will leave it unchanged. Therefore, the length of the minimized string is 3.
Example 2:
Input: s = "cbbd" Output: 3 Explanation: For this we can start with character 'b' at index 1. There is no occurrence of 'b' to the left of index 1, but there is one to the right at index 2, so we delete the 'b' at index 2. The string becomes "cbd" and further operations will leave it unchanged. Hence, the minimized length is 3.
Example 3:
Input: s = "dddaaa" Output: 2 Explanation: For this, we can start with the character 'd' at index 1. The closest occurrence of a 'd' to its left is at index 0, and the closest occurrence of a 'd' to its right is at index 2. We delete both index 0 and 2, so the string becomes "daaa". In the new string, we can select the character 'a' at index 2. The closest occurrence of an 'a' to its left is at index 1, and the closest occurrence of an 'a' to its right is at index 3. We delete both of them, and the string becomes "da". We cannot minimize this further, so the minimized length is 2.
Constraints:
1 <= s.length <= 100
s
contains only lowercase English letters
Solutions
Solution 1: Hash Table
The problem can actually be transformed into finding the number of different characters in the string. Therefore, we only need to count the number of different characters in the string.
The time complexity is $O(n)$, and the space complexity is $O(C)$. Here, $n$ is the length of the string, and $C$ is the size of the character set. In this problem, the character set is lowercase English letters, so $C=26$.

class Solution { public int minimizedStringLength(String s) { Set<Character> ss = new HashSet<>(); for (int i = 0; i < s.length(); ++i) { ss.add(s.charAt(i)); } return ss.size(); } }

class Solution { public: int minimizedStringLength(string s) { unordered_set<char> ss(s.begin(), s.end()); return ss.size(); } };

class Solution: def minimizedStringLength(self, s: str) > int: return len(set(s))

func minimizedStringLength(s string) int { ss := map[rune]struct{}{} for _, c := range s { ss[c] = struct{}{} } return len(ss) }

function minimizedStringLength(s: string): number { return new Set(s.split('')).size; }

use std::collections::HashMap; impl Solution { pub fn minimized_string_length(s: String) > i32 { let mut hash = HashMap::new(); for c in s.chars() { hash.insert(c, true); } hash.len() as i32 } }