What is the time and space complexity of Sequence Async Tasks?

Time complexity: O(n). Space complexity: O(n).

Sequence Async Tasks

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Solution Guide: Sequence Async Tasks

Approach

Use Array.reduce to chain promise-returning functions sequentially. Start with Promise.resolve([]) as the seed, and in each iteration call fn().then() to execute the next task only after the previous one resolves. Accumulate results in the carried array.

Complexity Analysis

Time: O(n)
Space: O(n)

Pattern

Promise Chain

Why It Works

Each reduce iteration returns a promise that chains onto the previous one, creating a linear dependency graph that ensures strictly sequential execution.

Updated Mar 2026