LC1544. Make The String Great

class Solution:
    def makeGood(self, s: str) -> str:
        stack = []
        for c in s:
            if stack and c.lower() == stack[-1].lower() and c != stack[-1]:
                stack.pop()
            else:
                stack.append(c)
        
        return "".join(stack)

Complexity

Time: $O(1)$
Space: $O(n)$