JS implementation of common algorithm in front-end

1. Bubble sort

function bubbleSort(arr){  var i = 0, j = 0; for(i=1; i<arr.length; i++){ for(j=0; j<=arr.length-i; j++){ var temp = 0; // ">" 从小到大排序 // "<" 从大到小排序 if(arr[j] > arr[j+1]){ temp = arr[j]; arr[j] = arr[j+1]; arr[j+1] = temp; } } } return arr;}

2. Quick Sort

function quickSort(arr,l,r){  if(l < r){ var i = l, j = r, x = arr[i]; while(i<j){ while(i<j && arr[j]>x) j--; if(i<j) //这里用i++，被换过来的必然比x小，赋值后直接让i自加，不用再比较，可以提高效率 arr[i++] = arr[j]; while(i<j && arr[i]<x) i++; if(i<j) //这里用j--，被换过来的必然比x大，赋值后直接让j自减，不用再比较，可以提高效率 arr[j--] = arr[i]; } arr[i] = x; quickSort(arr, l, i-1); quickSort(arr, i+1, r); }}

3, two-way merger

function merge(left, right) {    var result = [], il = 0, ir = 0; while (il < left.length && ir < right.length) { if (left[il] < right[ir]) { result.push(left[il++]); } else { result.push(right[ir++]); } } while(left[il]){ result.push(left[il++]); } while(right[ir]){ result.push(right[ir++]); } return result;}

String manipulation 1, judging palindrome string

functionPalindrome (STR) {\w matches any non-word character. Equivalent to "[^a-za-z0-9_]".var re =/[\w_]/g; //the string into lowercase characters and kills the character except the alpha-numeric var lowregstr = Str.tolowercase (). Replace (Re,//if the length of the string lowregstr is 0 o'clock, the string is palindrome if ( Lowregstr.length===0) return  True //if the first and last characters of the string are not the same, then the string is not palindrome if (lowregstr[< Span class= "Hljs-number" >0]!=lowregstr[lowregstr.length-1]) return FALSE; //recursive return palindrome (Lowregstr.slice ( 1,lowregstr.length-1));       

2, flip the string idea one: Backward traversal string

function reverseString(str){  var tmp = ‘‘; for(var i=str.length-1; i>=0; i--) tmp += str[i]; return tmp}

Idea two: Convert to array operation

function reverseString(str){  var arr = str.split(""); var i = 0,j = arr.length-1; while(i<j){ tmp = arr[i]; arr[i] = arr[j]; arr[j] = tmp; i++; j--; } return arr.join("");}

3. Generate random string of specified length

function randomString(n){  var str = ‘abcdefghijklmnopqrstuvwxyz0123456789‘; var tmp = ‘‘; for(var i=0; i<n; i++) { tmp += str.charAt(Math.round(Math.random()*str.length)); } return tmp;}

4. Maximum number of letters in the statistics string

functionFindmaxduplicatechar (STR) {if (str.length = =1) {return str;} var charobj = {}; for (var i = 0; i < str.length; i++ {if (!charobj[str.charat (i)]) {Charobj[str.charat (i)] = 1; Span class= "Hljs-keyword" >else {Charobj[str.charat (i)] + = 1;} var Maxchar =  ", MaxValue = 1; for (var k in charObj) {if (Charobj[k] >= maxValue) {Maxchar = k; maxValue = Charobj[k];}} return Maxchar +  ': ' + maxValue;}      

Array operation 1, array de-weight

function unique(arr){  var obj = {} var result = [] for(var i in arr){ if(!obj[arr[i]]){ obj[arr[i]] = true; result.push(arr[i]); } } return result;}

2, the maximum difference in the array

function getMaxProfit(arr){  var min = arr[0], max = arr[0]; for(var i = 0; i < arr.length; i++){ if(arr[i] < min) min = arr[i]; if(arr[i] > max) max = arr[i]; } return max - min;}

Other common algorithms 1, factorial non-recursive implementation

function factorialize(num) {  var result = 1; if(num < 0) return -1; if(num == 0 || num == 1) return 1; while(num>1) { result *= num--; } return result;}

Recursive implementation

function factorialize(num) {  var result = 1; if(num < 0) return -1; if(num == 0 || num == 1) return 1; if(num > 1) return num*factorialize(num-1);}

2, generate Fibonacci that cut the number of forced recursive implementation

functionGETFIB (N) { if (n = = 0) return 0; if (n = = 1) return 1; if (n > 1) return GETFIB (n-1) + GETFIB (n-2);} function Fibo (len) { var fibo = []; For (var i = 0; i < len; i++) {Fibo.push (Getfib (i));} return Fibo;}                  

Simple non-recursive implementation

function getFibonacci(n) {  var fibarr = []; var i = 0; while(i < n) { if(i <= 1) { fibarr.push(i); } else { fibarr.push(fibarr[i - 1] + fibarr[i - 2]) } i++; } return fibarr;}

3, two-part search for non-recursive implementation

function binary_search (arr, key) { var = 0, high = arr.length- 1; while (low <= high) { var mid = parseint (high + Low)/ 2); if (key = = Arr[mid]) { return mid;} Else if (key > Arr[mid]) {low = mid + 1;} Else if (Key < Arr[mid]) {high = mid -1;}} return -1;}                 

Recursive implementation

function binary_search2 (arr, Low, high, key) {if (Low > High)  return -1; var mid = parseint ((Low + high)/2) ; if (key = = Arr[mid]) {return mid;} else if (Key > Arr[mid]) { Return Binary_search2 (arr, Mid+1, high, key);} else if (Key < Arr[mid]) { Return BINARY_SEARCH2 (arr, Low, Mid-1, Key);}}       

JS implementation of common algorithms in front-end