快速排序的递归和非递归算法

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <stack>
using namespace std;
void quicksort(int* a, int from, int to);
void quicksort(int* a, int length);
void quicksort_nonrecursive(int* a, int from, int to);
int partition(int* a, int from, int to);

void quicksort(int* a, int from, int to)
{
if (from<to)
{
int pivot = partition(a, from, to);
quicksort(a, from, pivot-1);
quicksort(a, pivot+1, to);
}
}

void quicksort(int* a, int length)
{
return quicksort(a,0,length-1);
}

int partition(int* a, int from, int to)
{
int x = a[to];
int i = from-1;
for(int j = from; j<=to-1; ++j) {
if (a[j]<=x)
{
++i;
swap(a[i],a[j]);
}
}
swap(a[i+1],a[to]);
return i+1;
}

int main()
{
int i[9] = {3, 0, 6, 6, 7, 4, 6, 9, 8};
quicksort(i,9);
for(int j = 0; j<9; j++)
{
printf("%d\t",i[j]);
}
}

void quicksort_nonrecursive(int* a, int from, int to)
{
stack<int> simulate;
if (from<to)
{
int pivot = partition(a, from, to);
simulate.push(from);
simulate.push(pivot-1);
simulate.push(pivot+1);
simulate.push(to);
while (!simulate.empty())
{
to = simulate.top();
simulate.pop();
from = simulate.top();
simulate.pop();
pivot = partition(a, from, to);
if (from<pivot-1)
{
simulate.push(from);
simulate.push(pivot-1);
}
if (pivot+1<to)
{
simulate.push(pivot+1);
simulate.push(to);
}
}
}
}