LinkedList

[tipstar0125]

問題：https://atcoder.jp/contests/abc344/tasks/abc344_e 解答：https://atcoder.jp/contests/abc344/submissions/51213421

ライブラリ

#[derive(Debug)]
struct LinkedNode {
    front: Option<usize>,
    back: Option<usize>,
}

#[derive(Debug)]
struct LinkedList {
    list: HashMap<usize, LinkedNode>,
}

impl LinkedList {
    fn new(v: Vec<usize>) -> Self {
        let mut list = HashMap::new();
        if v.len() == 1 {
            list.insert(
                v[0],
                LinkedNode {
                    front: None,
                    back: None,
                },
            );
        } else if v.len() >= 2 {
            list.insert(
                v[0],
                LinkedNode {
                    front: None,
                    back: Some(v[1]),
                },
            );
            list.insert(
                v[v.len() - 1],
                LinkedNode {
                    front: Some(v[v.len() - 2]),
                    back: None,
                },
            );
            for i in 1..v.len() - 1 {
                list.insert(
                    v[i],
                    LinkedNode {
                        front: Some(v[i - 1]),
                        back: Some(v[i + 1]),
                    },
                );
            }
        }
        LinkedList { list }
    }
    fn remove(&mut self, x: usize) {
        let front = self.list[&x].front;
        let back = self.list[&x].back;
        if let Some(front) = front {
            if let Some(v) = self.list.get_mut(&front) {
                v.back = back;
            }
        }
        if let Some(back) = back {
            if let Some(v) = self.list.get_mut(&back) {
                v.front = front;
            }
        }
        self.list.remove(&x);
    }
    // xの直後にyを挿入
    fn insert(&mut self, x: usize, y: usize) {
        self.list.insert(
            y,
            LinkedNode {
                front: Some(x),
                back: self.list[&x].back,
            },
        );
        if let Some(back) = self.list[&x].back {
            if let Some(v) = self.list.get_mut(&back) {
                v.front = Some(y);
            }
        }
        if let Some(v) = self.list.get_mut(&x) {
            v.back = Some(y);
        }
    }
    fn to_list(&self) -> Vec<usize> {
        let mut ret = vec![];
        let mut now = {
            let mut head = 0;
            for (k, v) in self.list.iter() {
                if v.front.is_none() {
                    head = *k;
                    break;
                }
            }
            head
        };
        loop {
            ret.push(now);
            if let Some(x) = self.list[&now].back {
                now = x;
            } else {
                break;
            }
        }
        ret
    }
}