What is the time and space complexity of Implement _.once()?

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

Implement _.once()

Easy

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Solution Guide: Implement _.once()

Approach

Use a closure to track whether the function has been called via a boolean flag. On the first call, execute the function, store the result, and set the flag. On subsequent calls, return the cached result without re-executing.

Complexity Analysis

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

Pattern

Once Pattern

Why It Works

The closure captures a mutable boolean and result variable that persist across calls, ensuring the wrapped function body runs exactly once regardless of how many times the wrapper is invoked.

Updated Feb 2026