LeetCode 1087. Brace Expansion

Problem Statement

impl Solution {
    pub fn expand(s: String) -> Vec<String> {
        let (mut ans, mut prev) : (Vec<String>, Vec<String>) = (vec![], vec![]);
        let (mut in_brace, mut initialized) = (false, false);
        for c in s.chars() {
            if c == '{' {
                prev = ans.clone(); ans.clear();
                in_brace = true; continue;
            } else if c == '}' {
                in_brace = false;
                if !initialized {
                    initialized = true;
                }
                continue;
            } else if c == ',' {
                continue;
            }

            if in_brace {
                if !initialized {
                    ans.push(c.to_string());
                } else {
                    let mut cur = prev.clone();
                    for i in 0..cur.len() {
                        cur[i].push(c);
                    }
                    for str in cur {
                        ans.push(str);
                    }
                }
            } else {
                if !initialized {
                    ans.push(c.to_string());
                    initialized = true;
                } else {
                    for i in 0..ans.len() {
                        ans[i].push(c);
                    }
                }
            }
        }
        ans.sort();
        return ans;
    }
}