快速排序是實(shí)踐中最快的已知排序方法寺枉，平均性能在O(NlogN)括蝠，最快在O(N^2)
基本算法是采用分治法
1.將數(shù)組根據(jù)樞紐或衛(wèi)兵x来候，劃分成兩個(gè)子數(shù)組缸托，前面的子數(shù)組的所有元素<=x左敌，后面的>=x；
2.遞歸處理兩個(gè)子數(shù)組俐镐，遞歸邊界是有0個(gè)元素時(shí)矫限；
3.合并，無(wú)意義佩抹，已經(jīng)排好序了叼风。
以下是最簡(jiǎn)單的快排實(shí)現(xiàn)
function quicksort (A,s,e) {
if(s==undefined||e==undefined){
s=0;
e=A.length-1;
}
if(s<e){
var pivot = partition(s,e);
quicksort(A,0,pivot-1);
quicksort(A,pivot+1,e);
}
return A;
function partition(p,q){
var x = A[p];
var i = p;
for(var j=p+1;j<=q;j++){
if(A[j]<=x){
i++;
var temp = A[i];
A[i] = A[j];
A[j] = temp;
}
}
A[p] = A[i];
A[i] = x;
return i;
}
}
初始調(diào)用為quicksort([6,10,13,5,8,3,2,11],0,7)或quicksort([6,10,13,5,8,3,2,11])
#include <iostream>
#include <vector>
using namespace std;
int partition(int arr[],int p,int q){
int x = arr[p];
int i = p;
for (int j = p+1; j <= q; ++j)
{
if(arr[j]<=x){
i++;
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
arr[p] = arr[i];
arr[i] = x;
return i;
}
void quicksort(int arr[],int p,int q){
if(p<q){
int piv = partition(arr,p,q);
quicksort(arr,p,piv-1);
quicksort(arr,piv+1,q);
}
}
int partition2(int arr[],int p,int q){
int x = arr[p];
int i = p+1,j = q;
while(i<j){
while(arr[i]<=x){
i++;
}
while(arr[j]>x){
j--;
}
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
arr[p] = arr[j];
arr[j] = x;
}
void quicksort2(int arr[],int p,int q){
if(p<q){
int piv = partition2(arr,p,q);
quicksort(arr,p,piv-1);
quicksort(arr,piv+1,q);
}
}
int main(int argc, char const *argv[])
{
int arr[] = {6,10,13,5,8,3,2,11};
// quicksort(arr,0,7);
quicksort2(arr,0,7);
for (int i = 0; i < 8; ++i)
{
cout<<arr[i]<<"\t";
}
return 0;
}
