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Apply Transform Over Each Element in Array
Transform each element in an array based on a given function without using the built-in Array.map method.
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Easy · Apply Transform Over Each Element in Array core interview pattern
Answer-first summary
Transform each element in an array based on a given function without using the built-in Array.map method.
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To solve this problem, create a new array and apply the given function to each element of the array. Avoid using Array.map and instead manually perform the transformation, handling indices and values as needed.
Problem Statement
Given an array of integers and a function that maps each element, return a new array with each element transformed by that function.
The transformation should apply to each element such that returnedArray[i] = fn(arr[i], i), where the function takes both the value and index of the element into account.
Examples
Example 1
Input: arr = [1,2,3], fn = function plusone(n) { return n + 1; }
Output: [2,3,4]
const newArray = map(arr, plusone); // [2,3,4] The function increases each value in the array by one.
Example 2
Input: arr = [1,2,3], fn = function plusI(n, i) { return n + i; }
Output: [1,3,5]
The function increases each value by the index it resides in.
Example 3
Input: arr = [10,20,30], fn = function constant() { return 42; }
Output: [42,42,42]
The function always returns 42.
Constraints
- 0 <= arr.length <= 1000
- -109 <= arr[i] <= 109
- fn returns an integer.
Solution Approach
Manual Transformation Using Loops
You can loop over the array, apply the function to each element, and store the result in a new array. This avoids using the built-in map method and mimics its behavior.
Leverage Index for Transformation
Ensure that the function takes both the element and its index into account when performing the transformation, as this problem explicitly asks for index-based changes.
Handle Edge Cases
Consider edge cases like empty arrays or large arrays with extreme values. Ensure the solution is scalable and handles these without errors.
Complexity Analysis
| Metric | Value |
|---|---|
| Time | Depends on the final approach |
| Space | Depends on the final approach |
Time complexity depends on the approach, with the loop-based solution being O(n). Space complexity also depends on the approach, typically O(n) for the new array.
What Interviewers Usually Probe
- Can you apply the transformation manually without using Array.map?
- Do you understand the role of indices in applying the transformation?
- Are you able to identify edge cases like empty arrays or very large arrays?
Common Pitfalls or Variants
Common pitfalls
- Using Array.map instead of manually applying the transformation.
- Ignoring the index in the transformation function.
- Not handling edge cases such as an empty array or large integer values.
Follow-up variants
- Apply a similar transformation but with different types of functions.
- Handle larger arrays with performance optimizations.
- Modify the problem to return the transformed values using a different data structure.
FAQ
What is the core pattern in the 'Apply Transform Over Each Element in Array' problem?
The core pattern involves applying a transformation function to each element in an array manually, without using built-in array methods like Array.map.
How should I handle the indices of elements in this problem?
The problem specifically asks you to apply a transformation that uses both the element value and its index. Make sure to account for the index when transforming each element.
How can I avoid using Array.map?
Instead of Array.map, you should use a loop (for, while, etc.) to iterate through the array and manually build a new array with the transformed elements.
What are some common mistakes in this problem?
Common mistakes include using Array.map, not considering the element index, and failing to handle edge cases like empty arrays.
What other problem variants should I be prepared for?
Other variants include transformations with different function types, handling larger arrays efficiently, and using alternative data structures to store the transformed values.
Solution
Solution 1: traversal
We traverse the array $arr$, for each element $arr[i]$, replace it with $fn(arr[i], i)$. Finally, return the array $arr$.
function map(arr: number[], fn: (n: number, i: number) => number): number[] {
for (let i = 0; i < arr.length; ++i) {
arr[i] = fn(arr[i], i);
}
return arr;
}