Remove Duplicate Letters — LeetCode 316 Python Solution

The problem

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

Input

s = "bcabc"

Output

"abc"

Python solution

class Solution:
    def removeDuplicateLetters(self, s: str) -> str:
        last = {c: i for i, c in enumerate(s)}
        stk = []
        vis = set()
        for i, c in enumerate(s):
            if c in vis:
                continue
            while stk and stk[-1] > c and last[stk[-1]] > i:
                vis.remove(stk.pop())
            stk.append(c)
            vis.add(c)
        return ''.join(stk)

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 316. Remove Duplicate Letters is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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