What is the time and space complexity of Implement Promise.race?

Time complexity: O(n). Space complexity: O(1).

Implement Promise.race

Easy

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Solution Guide: Implement Promise.race

Approach

Wrap all promises in a new Promise and attach resolve/reject handlers to each one. The first promise to settle (fulfill or reject) triggers the outer promise, making it a race to the finish.

Complexity Analysis

Time: O(n)
Space: O(1)

Pattern

Promise Combinator

Why It Works

Since Promise.resolve/reject can only be called once, the first promise to settle wins and all subsequent settlements are ignored.

Updated Mar 2026