问题
I have been looking around the web for a while and I am wondering if there is a 'stable' defacto implementation of quicksort that is generally used? I can write my own but why reinvent the wheel...
回答1:
You can easily "stabilize" an unstable sort using a decorate-sort-undecorate pattern
function stableSort(v, f)
{
if (f === undefined) {
f = function(a, b) {
a = ""+a; b = ""+b;
return a < b ? -1 : (a > b ? 1 : 0);
}
}
var dv = [];
for (var i=0; i<v.length; i++) {
dv[i] = [v[i], i];
}
dv.sort(function(a, b){
return f(a[0], b[0]) || (a[1] - b[1]);
});
for (var i=0; i<v.length; i++) {
v[i] = dv[i][0];
}
}
the idea is to add the index as last sorting term so that no two elements are now "the same" and if everything else is the same the original index will be the discriminating factor.
回答2:
- Put your objects into an array.
Call Array.sort(). It's very fast.
var array = [3,7,2,8,2,782,7,29,1,3,0,34]; array.sort(); console.log(array); // prints [0, 1, 2, 2, 29, 3, 3, 34, 7, 7, 782, 8]
Why does that print in lexicographic order? That's how array.sort() works by default, e.g. if you don't provide a comparator function. Let's fix this.
var array = [3,7,2,8,2,782,7,29,1,3,0,34];
array.sort(function (a, b)
{
return a-b;
});
console.log(array); // prints [0, 1, 2, 2, 3, 3, 7, 7, 8, 29, 34, 782]
回答3:
Quicksort (recursive)
function quicksort(array) {
if (array.length <= 1) {
return array;
}
var pivot = array[0];
var left = [];
var right = [];
for (var i = 1; i < array.length; i++) {
array[i] < pivot ? left.push(array[i]) : right.push(array[i]);
}
return quicksort(left).concat(pivot, quicksort(right));
};
var unsorted = [23, 45, 16, 37, 3, 99, 22];
var sorted = quicksort(unsorted);
console.log('Sorted array', sorted);回答4:
A Functional equivalent
In celebration of Functional Javascript, which appears to be the in thing
at the moment, especially given ES6+ wonderful syntactic sugar additions. Arrow functions and destructuring I propose a very clean, short functional equivalent of the quicksort function. I have not tested it for performance or compared it to the built-in quicksort function but it might help those who are struggling to understand the practical use of a quicksort. Given its declarative nature it is very easy to see what is happening as oppose to how it works.
Here is a JSBin version without comments https://jsbin.com/zenajud/edit?js,console
function quickSortF(arr) {
// Base case
if (!arr.length) return []
// This is a ES6 addition, it uses destructuring to pull out the
// first value and the rest, similar to how other functional languages
// such as Haskell, Scala do it. You can then use the variables as
// normal below
const [head, ...tail] = arr,
// here we are using the arrow functions, and taking full
// advantage of the concise syntax, the verbose version of
// function(e) => { return e < head } is the same thing
// so we end up with the partition part, two arrays,
// one smaller than the pivot and one bigger than the
// pivot, in this case is the head variable
left = tail.filter( e => e < head),
right = tail.filter( e => e >= head)
// this is the conquer bit of divide-and-conquer
// recursively run through each left and right array
// until we hit the if condition which returns an empty
// array. These results are all connected using concat,
// and we get our sorted array.
return quickSortF(left).concat(head, quickSortF(right))
}
const q7 = quickSortF([11,8,14,3,6,2,7])
//[2, 3, 6, 7, 8, 11, 14]
const q8 = quickSortF([11,8,14,3,6,2,1, 7])
//[1, 2, 3, 6, 7, 8, 11, 14]
const q9 = quickSortF([16,11,9,7,6,5,3, 2])
//[2, 3, 5, 6, 7, 9, 11, 16]
console.log(q7,q8,q9)
The comments should provide enough if it is already not clear what is happening. The actual code is very short without comments, and you may have noticed I am not a fan of the semicolon. :)
回答5:
In this blog http://www.nczonline.net/blog/2012/11/27/computer-science-in-javascript-quicksort/ which has pointed out that Array.sort is implemented in quicksort or merge sort internaly.
Quicksort is generally considered to be efficient and fast and so is used by V8 as the implementation for Array.prototype.sort() on arrays with more than 23 items. For less than 23 items, V8 uses insertion sort[2]. Merge sort is a competitor of quicksort as it is also efficient and fast but has the added benefit of being stable. This is why Mozilla and Safari use it for their implementation of Array.prototype.sort().
and when using Array.sort,you should return -1 0 1 instead of true or false in Chrome.
arr.sort(function(a,b){
return a<b;
});
// maybe--> [21, 0, 3, 11, 4, 5, 6, 7, 8, 9, 10, 1, 2, 12, 13, 14, 15, 16, 17, 18, 19, 20, 22]
arr.sort(function(a,b){
return a > b ? -1 : a < b ? 1 : 0;
});
// --> [22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
回答6:
var array = [8, 2, 5, 7, 4, 3, 12, 6, 19, 11, 10, 13, 9];
quickSort(array, 0, array.length -1);
document.write(array);
function quickSort(arr, left, right)
{
var i = left;
var j = right;
var tmp;
pivotidx = (left + right) / 2;
var pivot = parseInt(arr[pivotidx.toFixed()]);
/* partition */
while (i <= j)
{
while (parseInt(arr[i]) < pivot)
i++;
while (parseInt(arr[j]) > pivot)
j--;
if (i <= j)
{
tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
i++;
j--;
}
}
/* recursion */
if (left < j)
quickSort(arr, left, j);
if (i < right)
quickSort(arr, i, right);
return arr;
}回答7:
Using ES6 rest, spread:
smaller = (a, list) => list.filter(x => x <= a)
larger = (a, list) => list.filter(x => x > a)
qsort = ([x, ...list]) => (!isNaN(x))
? [...qsort(smaller(x, list)), x, ...qsort(larger(x, list))]
: []
回答8:
Quick Sort (ES6)
function quickSort(arr) {
if (arr.length < 2) {
return arr;
}
const pivot = arr[Math.floor(Math.random() * arr.length)];
let left = [];
let right = [];
let equal = [];
for (let val of arr) {
if (val < pivot) {
left.push(val);
} else if (val > pivot) {
right.push(val);
} else {
equal.push(val);
}
}
return [
...quickSort(left),
...equal,
...quickSort(right)
];
}
Few notes:
- A random pivot keeps the algorithm efficient even when the data is sorted.
- As much as it nice to use
Array.filterinstead of usingfor ofloop, like some of the answers here, it will increase time complexity (Array.reducecan be used instead though).
回答9:
This algorithm work almost as fast as the default implementation of Array.prototype.sort in chrome.
function quickSort(t){
_quickSort(t,0,t.length-1,0,t.length-1);
}
function _quickSort(t, s, e, sp, ep){
if( s>=e ) return;
while( sp<ep && t[sp]<t[e] ) sp++;
if( sp==e )
_quickSort(t,s,e-1,s,e-1);
else{
while(t[ep]>=t[e] && sp<ep ) ep--;
if( sp==ep ){
var temp = t[sp];
t[sp] = t[e];
t[e] = temp;
if( s!=sp ){
_quickSort(t,s,sp-1,s,sp-1);
}
_quickSort(t,sp+1,e,sp+1,e);
}else{
var temp = t[sp];
t[sp] = t[ep];
t[ep] = temp;
_quickSort(t,s,e,sp+1,ep);
}
}
}
quickSort time (ms): 738
javaScriptSort time (ms): 603
var m = randTxT(5000,500,-1000,1000);
VS(m);
function VS(M){
var t;
t = Date.now();
for(var i=0;i<M.length;i++){
quickSort(M[i].slice());
}console.log("quickSort time (ms): "+(Date.now()-t));
t = Date.now();
for(var i=0;i<M.length;i++){
M[i].slice().sort(compare);
}console.log("javaScriptSort time (ms): "+(Date.now()-t));
}
function compare(a, b) {
if( a<b )
return -1;
if( a==b )
return 0;
return 1;
}
function randT(n,min,max){
var res = [], i=0;
while( i<n ){
res.push( Math.floor(Math.random()*(max-min+1)+min) );
i++;
}
return res;
}
function randTxT(n,m,min,max){
var res = [], i=0;
while( i<n ){
res.push( randT(m,min,max) );
i++;
}
return res;
}
回答10:
Yet another quick sort demonstration, which takes middle of the array as pivot for no specific reason.
const QuickSort = function (A, start, end) {
//
if (start >= end) {
return;
}
// return index of the pivot
var pIndex = Partition(A, start, end);
// partition left side
QuickSort(A, start, pIndex - 1);
// partition right side
QuickSort(A, pIndex + 1, end);
}
const Partition = function (A, start, end) {
if (A.length > 1 == false) {
return 0;
}
let pivotIndex = Math.ceil((start + end) / 2);
let pivotValue = A[pivotIndex];
for (var i = 0; i < A.length; i++) {
var leftValue = A[i];
//
if (i < pivotIndex) {
if (leftValue > pivotValue) {
A[pivotIndex] = leftValue;
A[i] = pivotValue;
pivotIndex = i;
}
}
else if (i > pivotIndex) {
if (leftValue < pivotValue) {
A[pivotIndex] = leftValue;
A[i] = pivotValue;
pivotIndex = i;
}
}
}
return pivotIndex;
}
const QuickSortTest = function () {
const arrTest = [3, 5, 6, 22, 7, 1, 8, 9];
QuickSort(arrTest, 0, arrTest.length - 1);
console.log("arrTest", arrTest);
}
//
QuickSortTest();
回答11:
This is it !!!
function typeCheck(a, b){
if(typeof a === typeof b){
return true;
}else{
return false;
}
}
function qSort(arr){
if(arr.length === 0){
return [];
}
var leftArr = [];
var rightArr = [];
var pivot = arr[0];
for(var i = 1; i < arr.length; i++){
if(typeCheck(arr[i], parseInt(0))){
if(arr[i] < pivot){
leftArr.push(arr[i]);
}else { rightArr.push(arr[i]) }
}else{
throw new Error("All must be integers");
}
}
return qSort(leftArr).concat(pivot, qSort(rightArr));
}
var test = [];
for(var i = 0; i < 10; i++){
test[i] = Math.floor(Math.random() * 100 + 2);
}
console.log(test);
console.log(qSort(test));
回答12:
Slim version:
function swap(arr,a,b){
let temp = arr[a]
arr[a] = arr[b]
arr[b] = temp
return 1
}
function qS(arr, first, last){
if(first > last) return
let p = first
for(let i = p; i < last; i++)
if(arr[i] < arr[last])
p += swap(arr, i, p)
swap(arr, p, last)
qS(arr, first, p - 1)
qS(arr, p + 1, last)
}
Tested with random values Arrays, and seems to be always faster than Array.sort()
回答13:
How about this non-mutating functional QuickSort:
const quicksort = (arr, comp, iArr = arr) => {
if (arr.length < 2) {
return arr;
}
const isInitial = arr.length === iArr.length;
const arrIndexes = isInitial ? Object.keys(arr) : arr;
const compF = typeof comp === 'function'
? comp : (left, right) => left < right ? -1 : right < left ? 1 : 0;
const [pivotIndex, ...indexesSansPivot] = arrIndexes;
const indexSortReducer = isLeftOfPivot => [
(acc, index) => isLeftOfPivot === (compF(iArr[index], iArr[pivotIndex]) === -1)
? acc.concat(index) : acc,
[]
];
const ret = quicksort(indexesSansPivot.reduce(...indexSortReducer(true)), compF, iArr)
.concat(pivotIndex)
.concat(quicksort(indexesSansPivot.reduce(...indexSortReducer(false)), compF, iArr));
return isInitial ? ret.reduce((acc, index) => acc.concat([arr[index]]), []) : ret;
};
As a bonus, it supports optional comparing function which enables sorting of array of objects per property/properties, and doesn't get slower if dealing with larger values/objects.
First quick sorts original array keys, then returns sorted copy of original array.
来源：https://stackoverflow.com/questions/5185864/javascript-quicksort