Array Prototype Last - Video Solutions

Problem Overview: You need to return the last element of an array. If the array is empty, return -1. In JavaScript, the task specifically asks you to extend Array.prototype with a last() method that behaves this way.

Approach 1: Prototype Method Enhancement (O(1) time, O(1) space)

This approach directly extends Array.prototype by adding a last() method. Inside the method, check the array length. If this.length === 0, return -1. Otherwise, access the last element using index this.length - 1. The key insight is that JavaScript arrays allow constant-time index access, so retrieving the final element requires no iteration. This solution follows the exact requirement of modifying the prototype and demonstrates understanding of JavaScript object behavior.

Approach 2: Utility Function with Direct Index Access (O(1) time, O(1) space)

In languages like C, C++, Java, Python, or C#, prototype modification is not relevant. Instead, implement a small helper function that accepts an array and returns its last element. Check if the array size is zero; if so, return -1. Otherwise, return the value at index n - 1. This relies on constant-time random access provided by arrays. The algorithm performs only a length check and a single index operation, keeping both time and space complexity constant.

Both solutions rely on the same core observation: the last element of an array is always accessible using the index length - 1. No traversal or additional data structures are required.

Recommended for interviews: The direct index access approach is what interviewers expect. It shows you understand array indexing and boundary conditions. When solving the JavaScript-specific version, implementing the Array.prototype.last method demonstrates familiarity with prototypes and built-in object extension. Both solutions run in O(1) time and O(1) space, which is optimal for this problem.