Leetcode - Remove Duplicate Letters (Python)

October 2020 Leetcode Challenge
Leetcode - Remove Duplicate Letters # 316

[stoup]

Great explanation, was able to make sense of it easily.

[janmichaelaustria]

it took me a while to figure out why answers for the example inputs were the way they were. nice video again Tim!

[treyi]

shouldn't the condition be while (stack and stack[-1] > s[i] and lookup(stack[-1]) > i )
because its a subsequence and we are removing only duplicate letters?

[oleksiimartens]

Time Complexity of this solution is O(n). We would need to remove 26 elements from the stack at most at each iteration which sets O(1) as the cost of an iteration

[sharifmansuri]

Thank you very much for this video. Sir I have a query, why we are not using sorted function. As following
s='dcabde'
l=sorted(set(s))
print (l)

[HD-xnbr]

I like this solution! It seems like we don't actually need to use the seen set though? I removed it entirely and it still passes all test cases. We can just check if s[i] is in the stack.

[sajiinsta]

how can i have just "a" in the output?i mean remove all two Consecutive letters
e.g:
input:hhoowaaaareyyoouu
expected output:wre

how can I do that?

[themagickalmagickman]

I feel silly for looking up the solution now, I shouldve been able to solve this. Need more determination

[samarthasthana]

Went the recursive way and regretted it :/