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We often encounter sorting problems when using js. This article will explain the js sorting problem in detail.
1. Bubble sorting
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 sorting
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 merge
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 operation
1. Determine the palindrome string
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. Flip the string
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 }
Idea 2: Convert into 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 a 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. Statistics of the most frequent letters in the string
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; }
Array operation
1. Array deduplication
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. 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 sequence
Forced recursive implementation
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; }
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. Binary search
Non-recursive implementation
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; }
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); } }
This article shows several codes for js sorting in detail. If you want to know more related knowledge, please pay attention to the PHP Chinese website.
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