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;
};
thank you for reading our best Algorithms to Improve your JavaScript Skills guide
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