2424-longest-uploaded-prefix.adoc

2424. Longest Uploaded Prefix

{leetcode}/problems/longest-uploaded-prefix/[LeetCode - 2424. Longest Uploaded Prefix ^]

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:

• 1 ⇐ n ⇐ 105

• 1 ⇐ video ⇐ n

• All values of video are distinct.

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

• At least one call will be made to longest.

思路分析

一刷

link:{sourcedir}/_2424_LongestUploadedPrefix.java[role=include]

参考资料