Top 10 Algorithms to Improve your JavaScript Skills




Top 10 Algorithms to Improve your JavaScript Skills

1. Find the missing number in the array

Input: [1, 2, 3, 4, 6, 7, 8, 9, 10]
Output: 5

const find_missing = function(input) {
  let n = input.length + 1;
let sum = 0;
  for (let i in input) {
    sum += input[i];
  }
return Math.floor((n * (n + 1)) / 2) - sum;
};

2. Inverting integers

Input: num = 123
Output: 321
Input: num = -123
Output: -321

const reverse = function(num) {
    let result = 0;
    while (num !== 0) {
      result = result * 10 + num % 10;
      // Math.trunc() method will remove the fractional part of the number and keep only the integer part
      num = Math.trunc(num / 10);
    }
if (result > 2**31 || result < -(2**31)) return 0;
    return result;
};

3. Array alignment

Input: [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

const permute = function(nums) {
    let results = [];
let go = (current) => {
      if (current.length === nums.length){
        results.push(current);
        return;
      }
      nums.forEach(n => {
        if (!current.includes(n)){
          go([...current, n]);
        }
      });
    }
    go([]);
    return results;
};

4. Alignment in strings

Input: s1 = “ab”, s2 = “eidbao”
Output: true
Input: s1 = “aa”, s2 = “eidbao”
Output: false

const checkPermutation = function(s1, s2) {
  const len1 = s1.length, len2 = s2.length;
  if (len1 > len2) return false;
const count = Array(26).fill(0);
  for (let i = 0; i < len1; i++) {
      count[s1.charCodeAt(i)-97]++;
      count[s2.charCodeAt(i)-97]--;
  }
  if (!count.some(e => e !== 0)) return true;
for (let i = len1; i < len2; i++) {
      count[s2.charCodeAt(i)-97]--;
      count[s2.charCodeAt(i-len1)-97]++;
      if (!count.some(e => e !== 0)) return true;
  }
  return false;
};

5. Longest valid brackets

Input: “(()”
Output: 2
Input: “)()())”
Output: 4

const longestValidParentheses = function(S) {
  let stack = [-1], ans = 0;
  for (let i = 0; i < S.length; i++)
    if (S[i] === '(') stack.push(i)
    else if (stack.length === 1) stack[0] = i
    else stack.pop(), ans = Math.max(ans, i - stack[stack.length-1])
  return ans
};

6. 4Sum

const fourSum = function(nums, target) {
  let result = [];
  let length = nums.length;
  if (length < 4) return result; 
  nums = nums.sort((a, b) => a - b );
for (let i = 0; i < length - 3; i++) {
    if (nums[i] === nums[i - 1]) continue;
    for (let j = i + 1; j < length - 2; j++) {
      if (j > i + 1 && nums[j] === nums[j - 1]) continue;
let k = j + 1;
      let l = length - 1;
while (k < l) {
        const sum = nums[i] + nums[j] + nums[k] + nums[l];
if (sum === target) {
          result.push([nums[i], nums[j], nums[k], nums[l]])
        }
if (sum <= target) {
          k += 1;
          while (nums[k] === nums[k - 1]) {
            k += 1;
          }
        }
if (sum >= target) {
          l -= 1;
          while (nums[l] === nums[l + 1]) {
            l -= 1;
          }
        }
      }
    }
  }
return result;
};

7. String multiplication

Input: num1 = “2”, num2 = “3”
Output: “6”

const multiply = function(num1, num2) {
 if (num1 == 0 || num2 == 0) return ‘0’;
 const result = [];
for (let a = num1.length — 1; a >= 0; a — ) {
 for (let b = num2.length — 1; b >= 0; b — ) {
 const p1 = a + b;
 const p2 = a + b + 1;
 const sum = (result[p2] ?? 0) + num1[a] * num2[b];
result[p1] = (result[p1] ?? 0) + Math.floor(sum / 10);
 result[p2] = sum % 10;
 }
 }
 result[0] == 0 && result.shift();
 return result.join(‘’);
};

8. Shortest Reply

Input: s = “aacecaaa”
Output: “aaacecaaa”
Input: s = “abcd”
Output: “dcbabcd”

const shortestPalindrome = function(s) {
  let index = 0;
  for (let i = s.length - 1; i >= 0; i--) {
    if (s[i] === s[index]) index++;
  }
  if (index === s.length) return s;
  let remainingRev = s.substring(index, s.length);
  console.log(remainingRev);
  remainingRev = reverse(remainingRev);
return remainingRev + shortestPalindrome(s.substring(0, index)) + s.substring(index);
};
function reverse(string) {
  let myString = '';
  for (let i = string.length - 1; i >= 0; i--) {
    myString = myString + string[i];
  }
  return myString;
};

9. Integers to English words

Input: num = 123
Output: “One Hundred Twenty Three”
Input: num = 1234567
Output: “One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven”

const numberToWords = function(num) {
  let result = toHundreds(num % 1000);
  const bigNumbers = ["Thousand", "Million", "Billion"];
  for (let i = 0; i < 3; ++i) {
    num = Math.trunc(num / 1000);
    result = num % 1000 !== 0 ? [toHundreds(num % 1000), bigNumbers[i], result].filter(Boolean).join(" ") : result;
  }
  return result.length === 0 ? "Zero" : result;
}
function toHundreds(num) {
  const numbers = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten",
    "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"];
  const tens = ["", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"];
  const result = Array(3).fill("");
  let a = Math.trunc(num / 100), b = num % 100, c = num % 10;
  result[0] = a > 0 && `${numbers[a]} Hundred`;
  result[1] = b < 20 ? numbers[b] : tens[Math.trunc(b / 10)]
  result[2] = b >= 20 && `${numbers[c]}`;
  return result.filter(Boolean).join(" ");
}

10. Ransom note

Input: ransomNote = “aa”, magazine = “ab”
Output: false
Input: ransomNote = “aa”, magazine = “aab”
Output: true

const canConstruct = function(ransomNote, magazine) {
 if (ransomNote.length > magazine.length) return false;
 let magMap = new Map();
for(let char of magazine) {
 magMap.set(char, (magMap.get(char) || 0 ) + 1);
 }
for(let note of ransomNote) {
 let counter = magMap.get(note);
 if (!counter) return false;
magMap.set(note, — counter);
 }
 return true;
};

 



Author Biography.

Editorial Team
Editorial Team

Content Writer

Join Our Newsletter.

Subscribe to CrowdforThink newsletter to get daily update directly deliver into your inbox.

CrowdforJobs is an advanced hiring platform based on artificial intelligence, enabling recruiters to hire top talent effortlessly.

CrowdforJobs

CrowdforApps brings to you the well researched list of the most successful and finest App development companies, Web software developers.

CrowdforApps

CrowdforGeeks is where lifelong learners come to learn the skills they need, to land the jobs they want, to build the lives they deserve.

CrowdforGeeks

CrowdforThink is a leading Indian media and information platform, known for its end-to-end coverage of the Indian startup ecosystem.

CrowdforThink
CFT

News & Blogs

f744dbf3ab03eaaa58fd3e6dac2d0169.png

How to Get User Country Name, Browser, OS Name,...

Using PHP get stoner details IP address country, device, cybersurfer, operating system  &nb...

ff7f9eca4d1a0d29656644f11b806865.png

How to Drag And Drop Data Between Two Tables In...

Introduction  occasionally you need to drag and drop data from one table to another table...

fd0e5c6e4196603ef85979b1bc50caf4.jpeg

Top 10 Amazing Books For Every Designers

There are innumerous books out there that can help you come a better developer, whether you are l...

Top Authors

Lamia Rochdi is the Marketing Manager at Bell Flavors & Fragrances EMEA. A successful family-...

Lamia Rochdi

I’m Mertin Wilson a technician in a camera company and certified expert of different P...

Mertin Wilson

Zakariya has recently joined the PakWheels team as a Content Marketing Executive, shortly after g...

Zakariya Usman

Overall 3+ years of experience as a Full Stack Developer with a demonstrated history of working i...

Lokesh Gupta
CFT

Our Client Says

WhatsApp Chat with Our Support Team