前端常见算法

1、冒泡排序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、快速排序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、二路归并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;}字符串操作1、判断回文字符串function palindrome(str){  // \W匹配任何非单词字符。等价于“[^A-Za-z0-9_]”。  var re = /[\W_]/g;  // 将字符串变成小写字符,并干掉除字母数字外的字符  var lowRegStr = str.toLowerCase().replace(re,'');  // 如果字符串lowRegStr的length长度为0时，字符串即是palindrome  if(lowRegStr.length===0) return true;  // 如果字符串的第一个和最后一个字符不相同，那么字符串就不是palindrome  if(lowRegStr[0]!=lowRegStr[lowRegStr.length-1]) return false;  //递归  return palindrome(lowRegStr.slice(1,lowRegStr.length-1));}2、翻转字符串思路一：反向遍历字符串function reverseString(str){  var tmp = '';  for(var i=str.length-1; i>=0; i--)    tmp += str[i];  return tmp}思路二：转化成array操作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、生成指定长度随机字符串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、统计字符串中次数最多字母function findMaxDuplicateChar(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;    } 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;}数组操作1、数组去重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、数组中最大差值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;}其他常见算法1、阶乘非递归实现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;}递归实现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、生成菲波那切数列强行递归实现function getfib(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;}简约非递归实现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、二分查找非递归实现function binary_search(arr, key) {  var low = 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;}递归实现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);  }}