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array prototype last core interview pattern Pattern

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database1 problemstune1/0/0 difficulty mixcategory0 linked topics

Pattern brief

Recognize first

Do you handle empty arrays explicitly to avoid undefined?

Solve rhythm

State the active state and invariant first, explain how each update preserves them, then pressure-test with counterexamples.

Most common miss

Accessing this[this.length] instead of this[this.length-1] causing undefined.

Recognition signals

Do you handle empty arrays explicitly to avoid undefined?
Are you modifying Array.prototype directly or using a helper function?

Solve flow

1. Define the active state/window.
2. Update state while preserving invariants.
3. Validate with edge-heavy examples.

Common misses

Accessing this[this.length] instead of this[this.length-1] causing undefined.

Recommended Ladder

Starter

Array Prototype Last

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2619

Array Prototype Last

Implement a method on all arrays that returns the last element or -1 for empty arrays, using Array.prototype correctly.

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