Leetcode JavaScript Problems

Introduction

The area of coding interviews and competitive programming is filled with questions that require you to be at your best. LeetCode is definitely an essential platform where developers perfect their technical ability and problem-solving skills. On LeetCode, a huge developer can find coding tasks varying from the simplest ones to the most complicated ones. It is just like a crucible where you can forge your algorithmic skills and learn how to use the data structures.

Among the mushrooming of programming languages for use, the choice comes to a very flexible one that has wide adoption, which is common in the development process of the web. This article is dedicated to LeetCode JavaScript problem selection, presenting useful techniques, strategies, and resources for problem-solving skill development for developers at intermediate or advanced levels.

Regardless of whether you're a veteran JavaScript programmer with the goal of being the master of problems related to algorithms or simply a fresher trying to embark on this journey of solving the problems on LeetCode's platform then, this guide intends to offer you the relevant knowledge and skills that will enable you to succeed. With the power of JavaScript, we are on a trip trying to uncover why the code puzzles are so tricky as we reveal the mysteries of the algorithms one by one into the World Wide Web.

Understanding LeetCode Problems

One of the prerequisite steps is a thorough (getting to know) of LeetCode problems' nature, in other words. Here, the issues are created to perform multi-attacks on the techniques of your coding skills, such as algorithmic efficiency, data structure operations, and problem analysis. Every issue usually has a definition, limitations, and examples in order to demonstrate the intended input-output. It would help if you took full time to get through these issues before you think of trying to solve them issues.

Strategies for Success:

  1. Start with Easy Problems: Whenever you are new to LeetCode or JavaScript, start with the easy problems for training and grasping the area. Study the basic algorithm structure, solve some simple entities, and update the system first, then proceed to the more advanced operation.
  2. Use Built-in Data Structures and Methods: JavaScript contains a large number of built-in data structures and functions that can make the data flow faster and more comfortably. Acquaint yourself with the arrays, objects, strings, and basic methods like map, filter, and reduce provided. Frequently relying on them not only helps to keep your solutions short but also makes them more efficient.
  3. Practice Algorithmic Techniques: While there are various solutions to problems on LeetCode, many of them can be solved using simple algorithmic techniques such as recursion, dynamic programming, greedy algorithms, and more. Please spend some time figuring these things out and putting them into the context of the different problems you practice.
  4. Optimize for Time and Space Complexity: LeetCode not only verifies the logic of your solution but also speeds it up. Note the time and space complexity of your algorithms; you also need to try to boost their performances. JS's ability to apply different optimization patterns (e.g., memorization, two-pointer, and Bitwise operations) can be utilized to great advantage.
  5. Test Your Solutions: LeetCode is a convenient tool for confirming that your solution works on the set of test data as much as possible. Explore these tricks to check your work and spot any errors. While paying attention to these scenarios, also be sure to address edge cases and corner scenarios so that you can never deny any bugs in the system.

Resources for Learning and Practice

  1. Official LeetCode Documentation: LeetCode even provides complete documentation, including a developers' manual explaining the data structure, algorithm, and coding patterns. Look at these resources to gain insights into different conflict resolution strategies.
  2. Online Courses and Tutorials: Hundreds of websites provide their own LeetCode courses and JavaScript tutorials that target interested learners. The internet has greatly influenced the way people prepare for technology-related interviews. Platforms such as Udemy, Coursera, and freeCodeCamp are examples of developers obtaining learning paths to cover a broad scope of coding interview questions.
  3. Community Forums and Discussions: Engage with and interact with developers' active community on platforms such as LeetCode discussion forum, Stack Overflow, and Reddit. It cannot be denied that engaging in discussions and opinions, peer review, and consulting those with richer experience in this field will aid you greatly when it comes to your education.

Problem 1:

Given an integer n, return true if it is a power of two. Otherwise, return false.

An integer n is a power of two if there exists an integer x such that n == 2^x.

Example 1:

Input: n = 1

Output: true

Explanation: 2^0 = 1

Example 2:

Input: n = 16

Output: true

Explanation: 2^4 = 16

Example 3:

Input: n = 3

Output: false

Constraints:

-231 <= n <= 231 - 1

JavaScript:

This procedure works by examining whether n has only one bit set to 1. It should n be a power of two; it will have only the first bit on, and the rest flipped after the first bit is set to 1. Hence, n & n-1 will yield a zero bitwise AND value for powers of two.

Problem 2:

Given a positive integer millis, write an asynchronous function that sleeps for millis milliseconds. It can resolve any value.

Example 1:

Input: millis = 100

Output: 100

Explanation: It should return a promise that resolves after 100ms.

let t = Date.now();

sleep(100).then(() => {

console.log(Date.now() - t); // 100

});

Example 2:

Input: millis = 200

Output: 200

Explanation: It should return a promise that resolves after 200ms.

Constraints:

1 <= millis <= 1000

JavaScript:

Output:

Output: 100
Elapsed time: 100
Output: 200
Elapsed time: 200

This code returns a Promise that is resolved after the wait period indicated in milliseconds. Then, a method is devised to handle the fulfilled value of the promise - in our case, it is the very millis parameter itself.

Problem 3:

Given an integer array nums, a reducer function fn, and an initial value init, return the final result obtained by executing the fn function on each element of the array, sequentially passing in the return value from the calculation on the preceding element.

This result is achieved through the following operations: val = fn(init, nums[0]), val = fn(val, nums[1]), val = fn(val, nums[2]), ... until every element in the array has been processed. The ultimate value of val is then returned.

If the length of the array is 0, the function should return init.

Please solve it without using the built-in Array.reduce method.

Example 1:

Input:

nums = [1,2,3,4]

fn = function sum(accum, curr) { return accum + curr; }

init = 0

Output: 10

Explanation:

Initially, the value is init=0.

(0) + nums[0] = 1

(1) + nums[1] = 3

(3) + nums[2] = 6

(6) + nums[3] = 10

The final answer is 10.

Example 2:

Input:

nums = [1,2,3,4]

fn = function sum(accum, curr) { return accum + curr * curr; }

init = 100

Output: 130

Explanation:

Initially, the value is init=100.

(100) + nums[0] * nums[0] = 101

(101) + nums[1] * nums[1] = 105

(105) + nums[2] * nums[2] = 114

(114) + nums[3] * nums[3] = 130

The final answer is 130.

Example 3:

Input:

nums = []

fn = function sum(accum, curr) { return 0; }

init = 25

Output: 25

Explanation: For empty arrays, the answer is always init.

Constraints:

0 <= nums.length <= 1000

0 <= nums[i] <= 1000

0 <= init <= 1000

JavaScript:

Output:

Output: 10
Output: 130
Output: 25

Problem 4:

Given an array of functions [f1, f2, f3, ..., fn], return a new function fn that is the function composition of the array of functions.

The function composition of [f(x), g(x), h(x)] is fn(x) = f(g(h(x))).

The function composition of an empty list of functions is the identity function f(x) = x.

Each function in the array accepts one integer as input and returns one integer as output.

Example 1:

Input: functions = [x => x + 1, x => x * x, x => 2 * x], x = 4

Output: 65

Explanation:

Evaluating from right to left ...

Starting with x = 4.

2 * (4) = 8

(8) * (8) = 64

(64) + 1 = 65

Example 2:

Input: functions = [x => 10 * x, x => 10 * x, x => 10 * x], x = 1

Output: 1000

Explanation:

Evaluating from right to left ...

10 * (1) = 10

10 * (10) = 100

10 * (100) = 1000

Example 3:

Input: functions = [], x = 42

Output: 42

Explanation:

The composition of zero functions is the identity function

Constraints:

-1000 <= x <= 1000

0 <= functions.length <= 1000

all functions accept and return a single integer

JavaScript:

Output:

Output: 65
Output: 1000
Output: 42

This code, composeFunctions function cycles over the array of functions in reverse order, forming the final this result by applying one function to the result of another function evaluation. Provided the array of functions is hollow, it returns the value x itself.

Problem 5:

Given an integer array arr and a mapping function fn, return a new array with a transformation applied to each element.

The returned array should be created such that returnedArray[i] = fn(arr[i], i).

Please solve it without the built-in Array.map method.

Example 1:

Input: arr = [1,2,3], fn = function plusone(n) { return n + 1; }

Output: [2,3,4]

Explanation:

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]

Explanation: 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]

Explanation: The function always returns 42.

Constraints:

0 <= arr.length <= 1000

-109 <= arr[i] <= 109

fn returns a number

JavaScript:

Output:

Output 1: [2, 3, 4]
Output 2: [1, 3, 5]
Output 3: [42, 42, 42]

This code specifies a map function that will create a new array called mappedArr and iterate over each element of the input array arr. The respective map function fn is applied to every element, and finally, the result is pushed to the mappedArr. At last, the element is mapped from the original array res, resulting in a new array called mappedArr containing the transformed elements.

Problem 6:

Given an array arr and a chunk size, return a chunked array. A chunked array contains the original elements in arr but consists of subarrays, each of length size. The length of the last subarray may be less than the size if arr.length is not evenly divisible by size.

You may assume the array is the output of JSON.parse. In other words, it is valid JSON.

Please solve it without using lodash's _.chunk function.

Example 1:

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

Output: [[1],[2],[3],[4],[5]]

Explanation: The arr has been split into subarrays, each with 1 element.

Example 2:

Input: arr = [1,9,6,3,2], size = 3

Output: [[1,9,6],[3,2]]

Explanation: The arr has been split into subarrays with 3 elements. However, only two elements are left for the 2nd subarray.

Example 3:

Input: arr = [8,5,3,2,6], size = 6

Output: [[8,5,3,2,6]]

Explanation: Size is greater than arr.length; thus, all elements are in the first subarray.

Example 4:

Input: arr = [], size = 1

Output: []

Explanation: There are no elements to be chunked, so an empty array is returned.

Constraints:

arr is a valid JSON array

2 <= JSON.stringify(arr).length <= 105

1 <= size <= arr.length + 1

JavaScript:

Output:

Output 1: [[1],[2],[3],[4],[5]]
Output 2: [[1,9,6],[3,2]]
Output 3: [[8,5,3,2,6]]
Output 4: []

This code is an example that uses chunkArray as the function name, which takes an array arr and a chunk size as parameters. It iterates through the array and splits it into subarrays of the length requested, putting each subarray into a new array called chunkedArray. At last, it gives you the chunkedArray.

Problem 7:

Create a class ArrayWrapper that accepts an array of integers in its constructor. This class should have two features:

When two instances of this class are added together with the + operator, the resulting value is the sum of all the elements in both arrays.

When the String() function is called on the instance, it returns a string separated by commas and surrounded by brackets, such as [1,2,3].

Example 1:

Input: nums = [[1,2],[3,4]], operation = "Add"

Output: 10

Explanation:

const obj1 = new ArrayWrapper([1,2]);

const obj2 = new ArrayWrapper([3,4]);

obj1 + obj2; // 10

Example 2:

Input: nums = [[23,98,42,70]], operation = "String"

Output: "[23,98,42,70]"

Explanation:

const obj = new ArrayWrapper([23,98,42,70]);

String(obj); // "[23,98,42,70]"

Example 3:

Input: nums = [[],[]], operation = "Add"

Output: 0

Explanation:

const obj1 = new ArrayWrapper([]);

const obj2 = new ArrayWrapper([]);

obj1 + obj2; // 0

Constraints:

0 <= nums.length <= 1000

0 <= nums[i] <= 1000

Note: nums is the array passed to the constructor

JavaScript:

Output:

Output 1: 10
Output 2: [23,98,42,70]
Output 3: 0

In this code, the forward class has a constructor that accepts an array of integers as an argument. It also has two methods: add() is the function that replaces the addition operator, and the result is the sum of all elements in both arrays, and toString() is a function that overrides the toString method, and thus the function returns a string surrounded by brackets, and in the middle, there is a comma separator.

Problem 8:

Write a function createHelloWorld. It should return a new function that always returns "Hello World."

Example 1:

Input: args = []

Output: "Hello World"

Explanation:

const f = createHelloWorld();

f(); // "Hello World"

The function returned by createHelloWorld should always return "Hello World".

Example 2:

Input: args = [{},null,42]

Output: "Hello World"

Explanation:

const f = createHelloWorld();

f({}, null, 42); // "Hello World"

Any arguments could be passed to the function, but it should still always return "Hello World".

Constraints:

0 <= args.length <= 10

JavaScript:

Output:

Output 1: Hello World
Output 2: Hello World

In this one, createHelloWorld() returns a new function that, when called, always returns "Hello World" no matter what. We generate instances of this function defined as createHelloWorld() and call them by providing different sets of arguments to show that the function returns "Hello World" irrespective of the passed arguments.

Problem 9:

Given a function fn, an array of arguments args, and a timeout t in milliseconds, return a cancel function cancelFn.

After a delay of cancelTimeMs, the returned cancel function cancelFn will be invoked.

setTimeout(cancelFn, cancelTimeMs)

Initially, the execution of the function fn should be delayed by t milliseconds.

If the function cancelFn is invoked before the delay of t milliseconds, it should cancel the delayed execution of fn. Otherwise, if cancelFn is not invoked within the specified delay t, fn should be executed with the provided arguments.

Example 1:

Input: fn = (x) => x * 5, args = [2], t = 20

Output: [{"time": 20, "returned": 10}]

Explanation:

const cancelTimeMs = 50;

const cancelFn = cancellable((x) => x * 5, [2], 20);

setTimeout(cancelFn, cancelTimeMs);

The cancellation was scheduled to occur after a delay of cancelTimeMs (50ms), which happened after the execution of fn(2) at 20ms.

Example 2:

Input: fn = (x) => x**2, args = [2], t = 100

Output: []

Explanation:

const cancelTimeMs = 50;

const cancelFn = cancellable((x) => x**2, [2], 100);

setTimeout(cancelFn, cancelTimeMs);

The cancellation was scheduled to occur after a delay of cancelTimeMs (50ms), which happened before the execution of fn(2) at 100ms, resulting in fn(2) never being called.

Example 3:

Input: fn = (x1, x2) => x1 * x2, args = [2,4], t = 30

Output: [{"time": 30, "returned": 8}]

Explanation:

const cancelTimeMs = 100;

const cancelFn = cancellable((x1, x2) => x1 * x2, [2,4], 30);

setTimeout(cancelFn, cancelTimeMs);

The cancellation was scheduled to occur after a delay of cancelTimeMs (100ms), which happened after the execution of fn(2,4) at 30ms.

Constraints:

fn is a function

args is a valid JSON array

1 <= args.length <= 10

20 <= t <= 1000

10 <= cancelTimeMs <= 1000

JavaScript:

Output:

For Example 1: [{"time": 20, "returned": 10}]
For Example 2: []
For Example 3: [{"time": 30, "returned": 8}]

The cancellable function in that code takes the main function fn, its arguments, but also the delay time t. It constructs a promise that resolves after t milliseconds and executes the function fn if it has yet to be canceled with the provided arguments. On the other hand, if a cancellation function is invoked before the timeout, the cancelled flag value is set to true. The plot is finally wrapped with an ending that may still need to be cancelled.






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