10大算法帮助你提高 JavaScript 技能
1、在数组中查找缺失的数字
输入：[1、2、3、4、6、7、8、9、10]
输出：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、取反整数
输入：数字 = 123
输出：321
输入：数字 = -123
输出：-321
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;};
3、阵列对齐
输入：[1,2,3]
输出：[[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、字符串对齐
输入：s1 = “ab”, s2 = “eidbao”
输出：true
输入：s1 = “aa”, s2 = “eidbao”
输出：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、最长有效括号
输入：”（（）”
输出：2
输入：”）（）（））”
输出：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] = ielse 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、字符串乘法
输入：num1 = “2”，num2 = “3”
输出：“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、最短回复
输入：s = “aacecaaa”
输出：“aaacecaaa”
输入：s = “abcd”
输出：“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、英文单词的整数
输入：数字 = 123
输出：“一百二十三”
输入：数字 = 1234567
输出：“一百万二百三十四五百六十七”
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
输入：ransomNote = “aa”，杂志 = “ab”
输出：false
输入：ransomNote = “aa”，杂志 = “aab”
输出：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;};
总结
以上就是我今天跟你分享的10个算法，希望对您有所帮助。