README.md

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.

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.

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

Solutions (Rust)

1. Solution

impl Solution {
    pub fn remove_duplicate_letters(s: String) -> String {
        let s = s.as_bytes();
        let mut mask = 0;
        let mut masks = vec![0; s.len()];
        let mut indices = vec![vec![]; 26];
        let mut i = 0;
        let mut ret = vec![];

        for j in (0..s.len()).rev() {
            masks[j] = mask;
            mask |= 1 << (s[j] - b'a');
            indices[(s[j] - b'a') as usize].push(j);
        }

        while mask != 0 {
            for j in (0..=26).filter(|x| mask & (1 << x) != 0) {
                let new_mask = mask ^ (1 << j);
                let k = match indices[j].binary_search_by(|x| i.cmp(x)) {
                    Ok(y) => indices[j][y],
                    Err(y) => indices[j][y - 1],
                };

                if masks[k] & new_mask == new_mask {
                    mask = new_mask;
                    i = k;
                    ret.push(b'a' + j as u8);
                    break;
                }
            }
        }

        String::from_utf8(ret).unwrap()
    }
}