Smallest Subsequence of Distinct Characters — LeetCode 1081 Python Solution

The problem

Given a string s, return the lexicographically smallest subsequence of s that contains all the distinct characters of s exactly once.

Example

Input

s = "bcabc"

Output

"abc"

Python solution

class Solution:
    def smallestSubsequence(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 1081. Smallest Subsequence of Distinct Characters 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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