DEV Community: pharia-le

Solving LeetCode - Remove Element

pharia-le — Sun, 20 Dec 2020 03:41:24 +0000

Question

Given an array nums and a value val, remove all instances of that value in-place and return the new length.

Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

The order of elements can be changed. It doesn't matter what you leave beyond the new length.

Clarification:

Confused why the returned value is an integer but your answer is an array?

Note that the input array is passed in by reference, which means a modification to the input array will be known to the caller as well.

Internally you can think of this:

// nums is passed in by reference. (i.e., without making a copy)
int len = removeElement(nums, val);

// any modification to nums in your function would be known by the caller.
// using the length returned by your function, it prints the first len elements.
for (int i = 0; i < len; i++) {
    print(nums[i]);
}

Example 1:

Input: nums = [3,2,2,3], val = 3
Output: 2, nums = [2,2]
Explanation: Your function should return length = 2, with the first two elements of nums being 2.
It doesn't matter what you leave beyond the returned length. For example if you return 2 with nums = [2,2,3,3] or nums = [2,2,0,0], your answer will be accepted.

Example 2:

Input: nums = [0,1,2,2,3,0,4,2], val = 2
Output: 5, nums = [0,1,4,0,3]
Explanation: Your function should return length = 5, with the first five elements of nums containing 0, 1, 3, 0, and 4. Note that the order of those five elements can be arbitrary. It doesn't matter what values are set beyond the returned length.

Constraints:

0 <= nums.length <= 100
0 <= nums[i] <= 50
0 <= val <= 100

Let's Go!

Solve by using PREP.

P - Two parameters. An array of numbers nums & a number val
R - Return the length of nums with numbers equal to val removed
E - Examples provided by question. (See Above)
P - See Below

var removeElement = function(nums, val) {
    // iterate over nums from last index to 0th
    // remove nums that equal val

    //return lengths of nums
};

Translate into code...

var removeElement = function(nums, val) {
    // iterate over nums from last index to 0th
    // remove nums that equal val
    for (let i=nums.length-1; i>=0; i--) {
        if (nums[i] === val) {
            nums.splice(i,1)
        }
    }

    //return lengths of nums
    return nums.length
};

Conclusion

& Remember... Happy coding, friends! =)

Sources

https://leetcode.com/problems/remove-element/

Solving LeetCode - Length of Last Word

pharia-le — Sun, 13 Dec 2020 06:32:22 +0000

Question

Given a string s consists of some words separated by spaces, return the length of the last word in the string. If the last word does not exist, return 0.

A word is a maximal substring consisting of non-space characters only.

Example 1:

Input: s = "Hello World"
Output: 5

Example 2:

Input: s = " "
Output: 0

Constraints:

<= s.length <= 104
s consists of only English letters and spaces ' '

Let's Go!

Solve by using PREP.

P - One parameter. A string s
R - Return number that represents length of last word in s
E - Examples provided by question. (See Above)
P - See Below

var lengthOfLastWord = function(s) {
    // remove whitespace & split s by empty space ' ' 
    // return the length of the last element of the array or 0
};

Translate into code...

var lengthOfLastWord = function(s) {
    // remove whitespace & split s by empty space ' ' 
    const words = s.trim().split(' ')
    // return the length of the last element of the array or 0
    return words.length > 0 ? words[words.length-1].length : 0
};

Conclusion

& Remember... Happy coding, friends! =)

Sources

https://leetcode.com/problems/length-of-last-word/

Solving LeetCode - Palindrome Number

pharia-le — Sun, 06 Dec 2020 05:03:06 +0000

Question

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Follow up: Could you solve it without converting the integer to a string?

Example 1:

Input: x = 121
Output: true

Example 2:

Input: x = -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Example 4:

Input: x = -101
Output: false

Constraints:

-231 <= x <= 231 - 1

Let's Go!

Solve by using PREP.

P - One parameter. A number x
R - Return true or false if palindrome
E - Examples provided by question. (See Above)
P - See Below

var isPalindrome = function(x) {
    // IF x is negative, RETURN false

    // Convert x to str and split into array
    // Invoke REDUCE method to reverse array and combine to single str
    // RETURN true or false based on comparing reversed str to x.toString()
};

Translate into code...

var isPalindrome = function(x) {
    // IF x is negative, RETURN false
    if (Math.sign(x) === -1) return false
    // Convert x to str and split into array
    // Invoke REDUCE method to reverse array and combine to single str
    // RETURN true or false based on comparing reversed str to x.toString()
    return x.toString().split('').reduce((rev, char) => char + rev) === x.toString()
};

Conclusion

& Remember... Happy coding, friends! =)

Sources

https://leetcode.com/problems/palindrome-number/

Solving LeetCode - Reverse Integer

pharia-le — Sun, 29 Nov 2020 03:58:19 +0000

Question

Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: x = 123
Output: 321

Example 2:

Input: x = -123
Output: -321

Example 3:

Input: x = 120
Output: 21

Example 4:

Input: x = 0
Output: 0

Constraints:

-231 <= x <= 231 - 1

Let's Go!

Solve by using PREP.

P - One parameter. A number x
R - Return the reverse of the number
E - Examples provided by question. (See Above)
P - See Below

var reverse = function(x) {
    const reversed = x
        .toString()
        .split('')
        .reverse()
        .join('');

    return parseInt(reversed) * Math.sign(x);
};

Translate into code...

var reverse = function(x) {
    // Convert x from number to string
    // Split string into array of elements
    // Apply reverse method
    // Join String
    const reversed = x
        .toString()
        .split('')
        .reverse()
        .join('');

    // Convert string to number & multiple by the sign of x
    // Return the above
    return parseInt(reversed) * Math.sign(x);
};

Conclusion

& Remember... Happy coding, friends! =)

Sources

https://leetcode.com/problems/reverse-integer/submissions/

Solving LeetCode - Median of Two Sorted Arrays

pharia-le — Sat, 21 Nov 2020 22:46:51 +0000

Question

Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.

Example 1:

Input: nums1 = [1,3], nums2 = [2]
Output: 2.00000
Explanation: merged array = [1,2,3] and median is 2.

Example 2:

Input: nums1 = [1,2], nums2 = [3,4]
Output: 2.50000
Explanation: merged array = [1,2,3,4] and median is (2 + 3) / 2 = 2.5.

Example 3:

Input: nums1 = [0,0], nums2 = [0,0]
Output: 0.00000

Example 4:

Input: nums1 = [], nums2 = [1]
Output: 1.00000

Example 5:

Input: nums1 = [2], nums2 = []
Output: 2.00000

Constraints:

nums1.length == m
nums2.length == n
0 <= m <= 1000
0 <= n <= 1000
1 <= m + n <= 2000
-106 <= nums1[i], nums2[i] <= 106

Let's Go!

Solve by using PREP.

P - Two parameters. Both are an array of integers (nums1 & nums2).
R - A number which represents the median of the combined arrays.
E - Examples provided by question. (See Above)
P - See Below

var findMedianSortedArrays = function(nums1, nums2) {
    // Use Reduce method to combines nums1 & nums2 to single array named data

    // Sort array from smallest to largest number

    // Return the below
    // Conditional if even or odd length data
      // If odd grab middle idx of data
      // Else even grab middle 2 numbers and divide by 2
};

Translate into code...

var findMedianSortedArrays = function(nums1, nums2) {
    // Use Reduce method to combines nums1 & nums2 to single array named data
    let data = nums1.reduce((result, num) => {
        result.push(num)
        return nums2
    }, nums2)

    // Sort array from smallest to largest number
    data.sort((a,b) => a - b)

    // Return the below
    // Conditional if even or odd length data
      // If odd grab middle idx of data
      // Else even grab middle 2 numbers and divide by 2
    if (data.length % 2 === 0) {
      return (data[data.length/2 - 1] + data[data.length/2]) / 2
    } else {
      return data[data.length / 2 - .5]
    }
};

Conclusion

& Remember... Happy coding, friends! =)

Sources

https://leetcode.com/problems/median-of-two-sorted-arrays/

Solving LeetCode - Longest Substring Without Repeating Characters

pharia-le — Sun, 15 Nov 2020 04:55:22 +0000

Question

Given a string s, find the length of the longest substring without repeating characters.

Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Constraints:

0 <= s.length <= 5 * 104
s consists of English letters, digits, symbols and spaces.

Let's Go!

Solve by using PREP.

P - One parameter of type string
R - A return of type number that represents the length of the longest substring that does not repeat characters
E - Examples provided by question. (See Above)
P - See Below

var lengthOfLongestSubstring = function(s) {
  // Assign i to 0 to track index of s
  // Assign count to [ 0 ] to track lengths of all substrings
  // Assign start to 0 to track the beginning idx of a new substring

  // Iterate over s while i < s.length
    // If slice of s from start to i does not include the current char at i of s
      // Add 1 to the last element of the count array
      // Add 1 to i
    // Else
      // Add a new length of 0 to last element of count array
      // Assign start and i to the previous index where the char at i of s appeared and then add 1

  // return the largest number within the count array
}

Translate into code...

var lengthOfLongestSubstring = function(s) {
  let start = 0
  let i = 0
  let count = [ 0 ]

  while (i < s.length) {
    if (!s.slice(start, i).includes(s.charAt(i))) {
      count[count.length - 1]++
      i++
    } else {
      count[count.length] = 0
      start, i = s.slice(0, i).lastIndexOf(s.charAt(i)) + 1
    }
  }

  return count.reduce((max, current) => current > max ? current : max)
}

Conclusion

& Remember... Happy coding, friends! =)

Sources

https://leetcode.com/problems/longest-substring-without-repeating-characters/

Solving LeetCode - Longest Substring Without Repeating Characters

pharia-le — Sun, 08 Nov 2020 00:30:31 +0000

Question

Given a string s, find the length of the longest substring without repeating characters.

Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Example 4:

Input: s = ""
Output: 0

Constraints:

0 <= s.length <= 5 * 104
s consists of English letters, digits, symbols and spaces.

Let's Go!

Solve by using PREP.

P - A string s of letters, digits, symbols and spaces
R - Return a number which is the length of the Longest Substring Without Repeating Characters
E - Examples provided by question. (See Above)
P - See Below

Attempt 1

var lengthOfLongestSubstring = function(s) {
    const arr = s.split('')
    let charMap = {}
    let count = [ 0 ]

    for (let i=0; i<arr.length; i++) {
        if (!charMap[arr[i]]) {
            count[count.length - 1] = count[count.length - 1]+1
            charMap[arr[i]] = 1
        } else {
            charMap = {}
            charMap[arr[i]] = 1
            count[count.length] = 1
        }
    }
    return count.reduce((max, current) => current > max ? current : max)
};

Results of Attempt 1

console.log(lengthOfLongestSubstring("abcabcbb")) // 3 - PASS
console.log(lengthOfLongestSubstring("aab")) // 2 - PASS
console.log(lengthOfLongestSubstring("dvdf")) // 2  - FAIL (CORRECT is 3)

To Be Continued...

Attempt 2...

Solving LeetCode - Add Two Numbers

pharia-le — Sun, 01 Nov 2020 01:54:24 +0000

Question

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Example 1:

Input: l1 = [2,4,3], l2 = [5,6,4]
Output: [7,0,8]
Explanation: 342 + 465 = 807.

Example 2:

Input: l1 = [0], l2 = [0]
Output: [0]

Example 3:

Input: l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9]
Output: [8,9,9,9,0,0,0,1]

Constraints:

The number of nodes in each linked list is in the range [1, 100].
0 <= Node.val <= 9
It is guaranteed that the list represents a number that does not have leading zeros.

Let's Go!

Solve by using PREP.

P - Two non-empty linked lists representing two non-negative integers.
R - Return a linked list of the two numbers added
E - Examples provided by question. (See Above)
P - See Below

Before I knew about Node List...

var addTwoNumbers = function(l1, l2) {
    const reverseOfL1 = reverseArr(l1)
    const reverseOfL2 = reverseArr(l2)
    let list = []
    let carry = 0

    for (let i=0; i<l1.length; i++) {
        const sum = reverseOfL1[i] + reverseOfL2[i]
        if (sum > 9) {
            list.push(sum%10+carry)
            carry = 1
        } else {
            list.push(sum+carry)
            carry = 0
        } 
    }

    return list
}

function reverseArr(arr) {
    return arr.reduce((newArr,num) => {
      newArr.unshift(num)
      return newArr
    }, [])
}

Realizing my mistake and reading up on NodeList and Linked Lists. Answer below:

let addTwoNumbers = function(l1, l2) {
    let dummyHead = new ListNode(0);
    let p1 = l1;
    let p2 = l2;
    let current = dummyHead;
    let carry = 0;

    while (p1 !== null || p2 !== null) {
        let x = (p1 !== null) ? p1.val : 0;
        let y = (p2 !== null) ? p2.val : 0;
        let sum = x + y + carry;

        carry = Math.floor(sum / 10);
        current.next = new ListNode(sum % 10);
        current = current.next;

        if (p1 !== null) {
            p1 = p1.next;
        }
        if (p2 !== null) {
            p2 = p2.next;
        }
    }

    if (carry > 0) {
        current.next = new ListNode(1);
    }

    return dummyHead.next;
};

Conclusion

& Remember... Happy coding, friends! =)

Sources

Solving LeetCode - Two Sum

pharia-le — Sun, 25 Oct 2020 04:00:43 +0000

Question

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

You can return the answer in any order.

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Output: Because nums[0] + nums[1] == 9, we return [0, 1].

Example 2:

Input: nums = [3,2,4], target = 6
Output: [1,2]

Example 3:

Input: nums = [3,3], target = 6
Output: [0,1]

Constraints:

2 <= nums.length <= 105
-109 <= nums[i] <= 109
-109 <= target <= 109
Only one valid answer exists.

Let's Go!

Solve by using PREP.

P - Two parameters. First is an array of integers (nums). Second is an integer (target).
R - An array of two integers which are the indices of the numbers that add to the target.
E - Examples provided by question. (See Above)
P - See Below

var twoSum = function(nums, target) {
  // Iterate over nums array with for loop where i is the indice of the first integer
    // Perform a second iteration starting from j where j is the is the indice of the next integer (j=i+1)
      // If nums[i] + nums[j] equals target integer
        // return [i, j] 
}

Translate into code...

var twoSum = function(nums, target) {
  // Iterate over nums array with for loop where i is the indice of the first element
    for (let i=0; i<nums.length; i++) {
    // Perform a second iteration where j is the is the indice of the second element
        for (let j=i+1; j<nums.length; j++) {
      // If nums[i] + nums[j] equals target integer
        // return [i, j] 
            if (nums[i] +nums[j] === target)
                return [i, j]
        }
    }
}

Conclusion

& Remember... Happy coding, friends! =)

Sources

https://leetcode.com/problems/two-sum/

Hoisting in JavaScript

pharia-le — Sat, 17 Oct 2020 22:19:58 +0000

What is Hoisting?

In JavaScript, hoisting is the terminology used to describe how a variable or function can be used before it has been declared.

Example:

console.log(name) // => undefined
var name = 'Pharia'

Conceptually we can imagine that the binding name is hoisted to the top of the code.

var name // declaration is moved to the top
console.log(name) // => undefined because all variables in JS are initially set to undefined
name = 'Pharia' // assignment is not moved

How is this possible?

In JavaScript, before code is executed line by line, the JS Engine will set aside memory space for the variables that you've created in that entire code you've built and all the functions you created as well. This is considered the compilation phase which will be followed by the execution phase.

for variables, only variables declared with the keyword var can be hoisted
for functions, a functions name identifier and body are all hoisted

Examples

var - CAN hoist

console.log(name) // undefined
var name = "Pharia"

const - CANNOT hoist

console.log(name) // // ReferenceError: Cannot access 'name' before initialization
const name = "Pharia"

let - CANNOT hoist

console.log(name) // ReferenceError: Cannot access 'name' before initialization
let name

variable declared with no keyword - CANNOT hoist

console.log(name) // ReferenceError: name is not defined
name = "Pharia"

function - CAN hoist

logName() // => "Pharia"
function logName() {
  return "Pharia"
}

Conclusion

Although hoisting is possible in Javascript, is it better practice to declare all your functions and variables at the top of their scope to avoid bugs &/or errors.

& Remember... Happy coding, friends! =)

Sources

Four Pillars of OOP

pharia-le — Sun, 11 Oct 2020 00:39:51 +0000

A brief overview of the four pills of Object-Oriented Programming (OOP)

Question

What are the four pillars of OOP?

Answer

The four pillars of OOP are encapsulation, abstraction, inheritance, and polymorphism.

Encapsulation

Encapsulation is the idea of containing the attributes and behaviors of a class within itself. The state is secured and is private to the class. Only the object itself can update the state, and other objects only have access to the object's state through public methods.

Abstraction

Abstraction is the way in which we select and present the pertinent information for an object. All the mechanisms under the hood need not be presented, but the high-level data will be.

Inheritance

Inheritance is a way in which an object acquires some/all of the properties of another object. It is a great way to reuse code and build on top of previously created objects.

Polymorphism

Polymorphism is distinct from inheritance because the object acquires some/all of the properties of another object, but the object will maintain its own unique methods and functions.

Conclusion

The four pillars are fundamental to OOP. Commit them to memory!

& Remember... Happy coding, friends! =)

Recursion Basics in JavaScript

pharia-le — Sat, 03 Oct 2020 23:13:40 +0000

What is Recursion?

The act of a function calling itself, recursion is used to solve problems that contain smaller sub-problems. A recursive function can receive two inputs: a base case (ends recursion) or a recursive case (resumes recursion). https://developer.mozilla.org/en-US/docs/Glossary/Recursion

A function that calls itself and has a base & recursive case. The function will essentially reinvoke itself until it arrives at a result.

Two Cases Explained

Base Case - At one point do we need to return our answer? When do we need to stop?
Recursive Case - How do we manipulate our argument or how can we adjust the argument for another reinvocation?

Example - countSheep()

Create a function countSheep() that outputs "1 sheep..." all the way up to the input number "x sheep..."

Let's solve by using the PREP technique

P - integer (x) for number of sheep, default argument of count = 0 to keep track of current sheep number
R - log out sheep from 1 to x
E - see below

// countSheep(3)
// 1 sheep...
// 2 sheep...
// 3 sheep...

P - see below

Base Case - return when all the sheep are counted (count === x)
Recursive Case - modify count by adding 1, return a console of the current count + a reinvocation w/ x and modified count

function countSheep(x, count=0) {
  // BASE CASE
  // return if count equals x, which means every sheep is counted

  // RECURSIVE CASE
  // modify argument by adding 1 to count
  // log current count & reinvoke w/ modification
}

Now, implement code logic.

function countSheep(x, count=0) {
  // BASE CASE
  // return if count equals x, which means every sheep is counted
  if (count === x ) return;

  // RECURSIVE CASE
  // modify argument by adding 1 to count
  count++
  // log current count & reinvoke w/ modification
  return console.log(x + ' sheep...') + countSheep(x, count)
}

Conclusion

When finding a recursive solution, always keep in mind what the base case and recursive case may be. It's a good way to start!

& Remember... Happy coding, friends! =)