快排 c语言实现

#include <stdio.h>


int split(int a[], int first, int last){
int pvt = a[first];
int left = first;                                                       // can't written as left = first + 1, which will cause error when first + 1 = last.
int right = last;
int tmp;
while(left < right){
while(a[right] > pvt){
--right;
}
while(left < right && a[left] <= pvt){
++left;
}
if(left < right){
tmp = a[left];
a[left] = a[right];
a[right] = tmp;
}
}
a[first] = a[right];
a[right] = pvt;
return right;
}


void qsort(int a[], int first, int last){
int pos;
if(first < last){
pos = split(a, first, last);
qsort(a, first, pos - 1);
qsort(a, pos + 1, last);
}
}


int main(){
int a[] = {2, 9, 5, 20, 4, 7, 2, 5};
int size = sizeof(a)/sizeof(int);
int i;
qsort(a, 0, size - 1);
for(i = 0; i < size; ++i){
printf("%d ", a[i]);
}
}