Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 26

Description

Remove Duplicate Letters

Given a string s, remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.

Example 1:

Input: s = "bcabc"
Output: "abc"

Example 2:

Input: s = "cbacdcbc"
Output: "acdb"

Constraints:

• 1 <= s.length <= 104
• s consists of lowercase English letters.

Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  string removeDuplicateLetters(string s) {
    vector<int> cnt(26);
    vector<int> used(26);
    for(auto c : s) {
      cnt[c - 'a'] += 1;
    }

    string answer;
    for(auto c : s) {
      if(used[c - 'a']) {
        cnt[c - 'a'] -= 1;
        continue;
      }
      while(answer.length() && answer.back() > c && cnt[answer.back() - 'a']) {
        used[answer.back() - 'a'] = false;
        answer.pop_back();
      }
      answer.push_back(c);
      used[c - 'a'] = true;
      cnt[c - 'a'] -= 1;
    }
    return answer;
  }
};

// Accepted
// 290/290 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 49.69 % of cpp submissions (6.9 MB)