Practice Longest Uploaded Prefix

Read the task, work through the examples, and check your approach against the constraints. Use the original LeetCode task for coding and submissions.

Medium#2424

LeetCode Problem

Longest Uploaded Prefix

Hash Table Binary Search Union Find Design Binary Indexed Tree Segment Tree Heap (Priority Queue)Ordered Set

Problem Statement

LUPrefix(n) tracks video IDs from 1 through n. upload(video) marks an ID uploaded. longest() returns the largest i such that every ID from 1 through i is uploaded, or zero if ID 1 is missing. Upload IDs are distinct. Practice approach: Store a boolean presence array and a prefix pointer. After an upload, move the pointer while its next ID is present. Each pointer position is visited once, so total advancement is O(n) and longest is O(1). The largest uploaded ID alone is not the prefix length.

Source: Longest Uploaded Prefix on LeetCode. Use the original task for its coding environment and submissions.

Examples

# Example 1

Input

["LUPrefix","upload","longest","upload","longest","upload","longest"]
[[3],[2],[],[3],[],[1],[]]

Output

[null,null,0,null,0,null,3]

Explanation

IDs 2 and 3 do not form a prefix until ID 1 arrives.

Constraints

1 <= n <= 10^5

1 <= video <= n

Upload IDs are distinct.

At most 2 * 10^5 total calls and at least one longest call.

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