Array Prototype Last - Practice Coding Problems

Array Prototype Last - Problem

JavaScript Easy

Write code that enhances all arrays such that you can call the array.last() method on any array and it will return the last element. If there are no elements in the array, it should return -1.

You may assume the array is the output of JSON.parse.

Note: This problem requires extending JavaScript's Array prototype with a custom method.

Input & Output

Example 1 — Basic Array

$ Input: arr = [1, 2, 3, 4, 5]

› Output: 5

💡 Note: The array has 5 elements, so the last element at index 4 is 5

Example 2 — Single Element

$ Input: arr = [10]

› Output: 10

💡 Note: Array with one element - the first and last element are the same

Example 3 — Empty Array

$ Input: arr = []

› Output: -1

💡 Note: Empty array has no elements, so return -1 as specified

Constraints

0 ≤ arr.length ≤ 1000
-1000 ≤ arr[i] ≤ 1000

Visualization

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Understanding the Visualization

Input Array

Given array with elements to process

Find Last

Locate the last element using array length

Return Result

Return last element or -1 if empty

Key Takeaway

🎯 Key Insight: Use array length to directly access the last element in O(1) time

Asked in

G Google 25 a Amazon 20 f Facebook 15

The key insight is that we can use the array's length property to directly access the last element at index length - 1. The optimal approach uses direct indexing with O(1) time and O(1) space complexity.

Common Approaches

Approach	Time	Space	Notes
✓ Direct Index Access	O(1)	O(1)	Use array length to directly access the last element
Linear Scan	O(n)	O(1)	Iterate through entire array to find the last element

Direct Index Access — Algorithm Steps

Step 1: Check if array is empty
Step 2: Access element at index (length - 1)
Step 3: Return the element or -1 if empty

Visualization

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Step-by-Step Walkthrough

Check Length

Get array size to calculate last index

Calculate Index

Last index = length - 1

Direct Access

Return arr[lastIndex] immediately

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int solution(int* arr, int size) {
    if (size == 0) {
        return -1;
    }
    return arr[size - 1];
}

int main() {
    char line[1000];
    fgets(line, sizeof(line), stdin);
    
    int arr[100];
    int size = 0;
    
    char* token = strtok(line, "[],\n ");
    while (token != NULL) {
        arr[size++] = atoi(token);
        token = strtok(NULL, "[],\n ");
    }
    
    printf("%d\n", solution(arr, size));
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Direct array access using index is constant time

✓ Linear Growth

Space Complexity

O(1)

No extra space needed beyond a single variable

✓ Linear Space

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Smart Actions

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Direct Index Access — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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