LeetCode 1047. Remove All Adjacent Duplicates In String



You are given a string s consisting of lowercase English letters. A duplicate removal consists of choosing two adjacent and equal letters and removing them.

We repeatedly make duplicate removals on s until we no longer can.

Return the final string after all such duplicate removals have been made. It can be proven that the answer is unique.

Example 1:

Input: s = "abbaca"
Output: "ca"
For example, in "abbaca" we could remove "bb" since the letters are adjacent and equal, and this is the only possible move.  The result of this move is that the string is "aaca", of which only "aa" is possible, so the final string is "ca".

Example 2:

Input: s = "azxxzy"
Output: "ay"


  • 1 <= s.length <= 105
  • s consists of lowercase English letters.


We can use a stack to solve this problem. We only push the non duplicated adjacent character into the stack.

Python Solution

class Solution:
    def removeDuplicates(self, s: str) -> str:
        stack = []
        for c in s:
            if len(stack) > 0 and c == stack[-1]:
        return "".join(stack)
  • Time Complexity: O(N).
  • Space Complexity: O(N).

where Q is the length of queries and N is the length of colors.

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