316. Remove Duplicate Letters

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.

Note: This question is the same as 1081: <https://leetcode.comhttps://leetcode.com/problems/smallest-subsequence-of-distinct-characters/>

Example 1:

Input: s = "bcabc"
Output: "abc"

Example 2:

Input: s = "cbacdcbc"
Output: "acdb"

Constraints:

• 1 <= s.length <= 104
• s consists of lowercase English letters.

# @lc code=start
using LeetCode

function remove_duplicate_letters(s::String)::String
    stk = Char[]
    added = Set{Char}()
    remain = fill(0, 26)
    for ch in s
        remain[ch - 'a' + 1] += 1
    end
    for ch in s
        if !(ch in added)
            while !isempty(stk) && stk[end] > ch && remain[stk[end] - 'a' + 1] > 0
                pop!(added, pop!(stk))
            end
            push!(added, ch)
            push!(stk, ch)
        end
        remain[ch - 'a' + 1] -= 1
    end
    return join(stk)
end
# @lc code=end

remove_duplicate_letters (generic function with 1 method)

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