1656. Design an Ordered Stream

#Problem

There is a stream of n (idKey, value) pairs arriving in an arbitrary order, where idKey is an integer between 1 and n and value is a string. No two pairs have the same id.

Design a stream that returns the values in increasing order of their IDs by returning a chunk (list) of values after each insertion. The concatenation of all the chunks should result in a list of the sorted values.

Implement the OrderedStream class:

• OrderedStream(int n) Constructs the stream to take n values.
• String[] insert(int idKey, String value) Inserts the pair (idKey, value) into the stream, then returns the largest possible chunk of currently inserted values that appear next in the order.

https://leetcode.cn/problems/design-an-ordered-stream/

Example 1:

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

cpp

// Note that the values ordered by ID is ["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"].
// Concatentating all the chunks returned:
// [] + ["aaaaa"] + ["bbbbb", "ccccc"] + [] + ["ddddd", "eeeee"] = ["aaaaa", "bbbbb", "ccccc", "ddddd", "eeeee"]
// The resulting order is the same as the order above.

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.

#Test Cases

class OrderedStream:

    def __init__(self, n: int):


    def insert(self, idKey: int, value: str) -> List[str]:



# Your OrderedStream object will be instantiated and called as such:
# obj = OrderedStream(n)
# param_1 = obj.insert(idKey,value)

import pytest

from solution import OrderedStream

null = None


@pytest.mark.parametrize('actions, params, expects', [
    (
        ["OrderedStream", "insert", "insert", "insert", "insert", "insert"],
        [[5], [3, "ccccc"], [1, "aaaaa"], [2, "bbbbb"], [5, "eeeee"], [4, "ddddd"]],
        [null, [], ["aaaaa"], ["bbbbb", "ccccc"], [], ["ddddd", "eeeee"]],
    ),
])
@pytest.mark.parametrize('clazz', [OrderedStream])
def test_solution(clazz, actions, params, expects):
    sol = None
    for action, args, expected in zip(actions, params, expects):
        if action == 'OrderedStream':
            sol = clazz(*args)
        else:
            assert getattr(sol, action)(*args) == expected

#Thoughts

用长度为 n 的数组用于记录 stream 的所有值，用一个遍历 ptr 记录下一次可以返回的 stream 部分的起始位置。每次 insert 的时候，先把给定的值存入给定的位置，如果 ptr 与该位置相同，则可以输出一部分内容（从 ptr 开始直到下一个为赋值的位置为止），否则直接返回空。

构造方法时间复杂度 O(n)，空间复杂度 O(n)。n 次调用 insert 方法，总的时间复杂度为 O(n)。

#Code

class OrderedStream:

    def __init__(self, n: int):
        self._n = n
        self._store: list[str|None] = [None] * n
        self._ptr = 0

    def insert(self, idKey: int, value: str) -> list[str]:
        idKey -= 1
        self._store[idKey] = value
        if self._ptr != idKey:
            return []

        while self._ptr < self._n and self._store[self._ptr] is not None:
            self._ptr += 1

        return self._store[idKey:self._ptr]


# Your OrderedStream object will be instantiated and called as such:
# obj = OrderedStream(n)
# param_1 = obj.insert(idKey,value)