2424 - Longest Uploaded Prefix.

Medium

You are given a stream of n videos, each represented by a distinct number from 1 to n that you need to "upload" to a server. You need to implement a data structure that calculates the length of the longest uploaded prefix at various points in the upload process.

We consider i to be an uploaded prefix if all videos in the range 1 to i ( inclusive ) have been uploaded to the server. The longest uploaded prefix is the maximum value of i that satisfies this definition.

Implement the LUPrefix class:

• LUPrefix(int n) Initializes the object for a stream of n videos.

• void upload(int video) Uploads video to the server.

• int longest() Returns the length of the longest uploaded prefix defined above.

Example 1:

Input

"LUPrefix", "upload", "longest", "upload", "longest", "upload", "longest"

[4, 3, [], 1, [], 2, []]

Output: null, null, 0, null, 1, null, 3

Explanation:

LUPrefix server = new LUPrefix(4); // Initialize a stream of 4 videos.
server.upload(3); // Upload video 3.
server.longest(); // Since video 1 has not been uploaded yet, there is no prefix.
                  // So, we return 0.
server.upload(1); // Upload video 1.
server.longest(); // The prefix [1] is the longest uploaded prefix, so we return 1.
server.upload(2); // Upload video 2.
server.longest(); // The prefix [1,2,3] is the longest uploaded prefix, so we return 3.

Constraints:

• <code>1 <= n <= 10⁵</code>

• 1 <= video <= n

• All values of video are distinct.

• At most <code>2 * 10⁵</code> calls in total will be made to upload and longest.

• At least one call will be made to longest.