1.霍尔法

#include <iostream>
using namespace std;
int partition(int *arr,int left,int right){
	int pivotIndex=left;
	while(left<right){
		while(left<right && arr[right]>=arr[pivotIndex]){
			right--;
		}
		while(left<right && arr[left]<=arr[pivotIndex]){
			left++;
		}
		swap(arr[left],arr[right]);
	}
	swap(arr[left],arr[pivotIndex]);
	return left;
}
void quicksort(int *arr,int left,int right){
	if(left<right){
		int pivotIndex=partition(arr,left,right);
		quicksort(arr,left,pivotIndex-1);
		quicksort(arr,pivotIndex+1,right);
	}
}
int main(){
	int n;
    cin>>n;
    int arr[100005];
    for(int i=0;i<n;i++){
    	cin>>arr[i];
	}
    quicksort(arr,0,n-1);
    for(int i=0;i<n;i++){
    	cout<<arr[i]<<" ";
	}
	return 0;
} 

2. 竞赛用

题目链接：https://www.luogu.com.cn/problem/P1177

#include <iostream>
using namespace std;
void quicksort(int *arr,int left,int right){
	if(left>=right) return;
	int l=left-1,r=right+1,pivot=arr[(left+right)/2];
	while(l<r){
		do l++;while(arr[l]<pivot);
		do r--;while(arr[r]>pivot);
		if(l<r) swap(arr[l],arr[r]);
	}
	quicksort(arr,left,r);
	quicksort(arr,r+1,right);
}

int main(){
	int n;
	cin>>n;
	int arr[100005];
	for(int i=0;i<n;i++){
		cin>>arr[i];
	}
	quicksort(arr,0,n-1);
	for(int i=0;i<n;i++){
		cout<<arr[i]<<" ";
	}
	return 0;
}