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.

Example:

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

Explanation
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"].

Constraints:

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.

Solution:

class OrderedStream {
    Map<Integer, String> map;
    int ptr;
    int n;
    
    public OrderedStream(int n) {
        map = new HashMap();    
        ptr = 1;
        this.n = n;
    }
    
    public List<String> insert(int id, String value) {
        map.put(id, value);
        List<String> res = new ArrayList();
        if (map.containsKey(ptr)) {
            int i = ptr;
            for (; i <= this.n; i ++) {
                if (map.containsKey(i)) {
                    res.add(map.get(i));
                } else {
                    break;
                }
            }
            ptr = i;
        }
        return res;
    }
}

/**
 * Your OrderedStream object will be instantiated and called as such:
 * OrderedStream obj = new OrderedStream(n);
 * List<String> param_1 = obj.insert(id,value);
 */