Top 7 best Algorithms to Improve your JavaScript Skills🚀 🚀

Today I will teach you top 7 best algorithms to improve your JavaScript skills

best Algorithms to Improve JavaScript Skills as programmer

so let's start to understand JavaScript algorithms

1. how to Find the missing number from the array

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;
};

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

2. Inverting integers in JavaScript

const reverse = function(num) {
    let result = 0;
    while (num !== 0) {
      result = result * 10 + num % 10;
      // Math.trunc() 方法会将数字的小数部分去掉，只保留整数部分
      num = Math.trunc(num / 10);
    }
if (result > 2**31 || result < -(2**31)) return 0;
    return result;
};

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

3.Array alignment

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;
};

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

4.Alignment in strings

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;
};

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

5.Longest valid brackets

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
};

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

6.String multiplication

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(‘’);
};

Input: num1 = “2”, num2 = “3”
Output: “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;
};

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