1656. Design an Ordered Stream

There are n (id, value) pairs, where id is an integer between 1 and n and value is a string. No two pairs have the same id.

Design a stream that takes the n pairs in an arbitrary order, and returns the values over several calls in increasing order of their ids.

Implement the OrderedStream class:

  • OrderedStream(int n) Constructs the stream to take n values and sets a current ptr to 1.
  • String[] insert(int id, String value) Stores the new (id, value) pair in the stream. After storing the pair:
    • If the stream has stored a pair with id = ptr, then find the longest contiguous incrementing sequence of ids starting with id = ptr and return a list of the values associated with those ids in order. Then, update ptr to the last id + 1.
    • Otherwise, return an empty list.



["OrderedStream", "insert", "insert", "insert", "insert", "insert"]
[[5], [3, "ccccc"], [1, "aaaaa"], [2, "bbbbb"], [5, "eeeee"], [4, "ddddd"]]
[null, [], ["aaaaa"], ["bbbbb", "ccccc"], [], ["ddddd", "eeeee"]]

OrderedStream os= new OrderedStream(5);
os.insert(3, "ccccc"); // Inserts (3, "ccccc"), returns [].
os.insert(1, "aaaaa"); // Inserts (1, "aaaaa"), returns ["aaaaa"].
os.insert(2, "bbbbb"); // Inserts (2, "bbbbb"), returns ["bbbbb", "ccccc"].
os.insert(5, "eeeee"); // Inserts (5, "eeeee"), returns [].
os.insert(4, "ddddd"); // Inserts (4, "ddddd"), returns ["ddddd", "eeeee"].



  • 1 <= n <= 1000
  • 1 <= id <= n
  • value.length == 5
  • value consists only of lowercase letters.
  • Each call to insert will have a unique id.
  • Exactly n calls will be made to insert.

Rust Solution

use std::collections::HashMap;
struct OrderedStream {
    ptr: i32,
    pairs: HashMap<i32, String>,
    n: i32,

impl OrderedStream {
    fn new(n: i32) -> Self {
        let pairs = HashMap::new();
        let ptr = 1;
        OrderedStream { ptr, pairs, n }

    fn insert(&mut self, id: i32, value: String) -> Vec<String> {
        self.pairs.insert(id, value);
        let mut res = vec![];
        if self.ptr == id {
            for i in id..=self.n {
                if let Some(v) = self.pairs.get(&i) {
                    self.ptr += 1;
                } else {

fn test() {
    let mut obj = OrderedStream::new(5);
    assert_eq!(obj.insert(3, "ccccc".to_string()), vec_string![]);
    assert_eq!(obj.insert(1, "aaaaa".to_string()), vec_string!["aaaaa"]);
        obj.insert(2, "bbbbb".to_string()),
        vec_string!["bbbbb", "ccccc"]
    assert_eq!(obj.insert(5, "eeeee".to_string()), vec_string![]);
        obj.insert(4, "ddddd".to_string()),
        vec_string!["ddddd", "eeeee"]

Having problems with this solution? Click here to submit an issue on github.