316. Remove Duplicate Letters LeetCode Solution

In this guide, you will get 316. Remove Duplicate Letters LeetCode Solution with the best time and space complexity. The solution to Remove Duplicate Letters problem is provided in various programming languages like C++, Java, and Python. This will be helpful for you if you are preparing for placements, hackathons, interviews, or practice purposes. The solutions provided here are very easy to follow and include detailed explanations.

Table of Contents

1. Problem Statement
2. Complexity Analysis
3. Remove Duplicate Letters solution in C++
4. Remove Duplicate Letters solution in Java
5. Remove Duplicate Letters solution in Python
6. Additional Resources

Problem Statement of 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/

Complexity Analysis

• Time Complexity: O(n)
• Space Complexity: O(n)

316. Remove Duplicate Letters LeetCode Solution in C++

class Solution {
 public:
  string removeDuplicateLetters(string s) {
    string ans;
    vector<int> count(128);
    vector<bool> used(128);

    for (const char c : s)
      ++count[c];

    for (const char c : s) {
      --count[c];
      if (used[c])
        continue;
      while (!ans.empty() && ans.back() > c && count[ans.back()] > 0) {
        used[ans.back()] = false;
        ans.pop_back();
      }
      used[c] = true;
      ans.push_back(c);
    }

    return ans;
  }
};
/* code provided by PROGIEZ */

316. Remove Duplicate Letters LeetCode Solution in Java

class Solution {
  public String removeDuplicateLetters(String s) {
    StringBuilder sb = new StringBuilder();
    int[] count = new int[128];
    boolean[] used = new boolean[128];

    for (final char c : s.toCharArray())
      ++count[c];

    for (final char c : s.toCharArray()) {
      --count[c];
      if (used[c])
        continue;
      while (sb.length() > 0 && last(sb) > c && count[last(sb)] > 0) {
        used[last(sb)] = false;
        sb.setLength(sb.length() - 1);
      }
      used[c] = true;
      sb.append(c);
    }

    return sb.toString();
  }

  private char last(StringBuilder sb) {
    return sb.charAt(sb.length() - 1);
  }
}
// code provided by PROGIEZ

316. Remove Duplicate Letters LeetCode Solution in Python

class Solution:
  def removeDuplicateLetters(self, s: str) -> str:
    ans = []
    count = collections.Counter(s)
    used = [False] * 26

    for c in s:
      count[c] -= 1
      if used[string.ascii_lowercase.index(c)]:
        continue
      while ans and ans[-1] > c and count[ans[-1]] > 0:
        used[ord(ans[-1]) - ord('a')] = False
        ans.pop()
      ans.append(c)
      used[ord(ans[-1]) - ord('a')] = True

    return ''.join(ans)
 # code by PROGIEZ

Additional Resources

• Explore all LeetCode problem solutions at Progiez here
• Explore all problems on LeetCode website here

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