C/C++中的递归与非递归排序
[代码] 普通递归算法
#include <iostream>
using namespace std;
int partition(int *a, int l, int h){
int x = a[l];
int i = l;
int j = h+1;
int temp;
while (i<j){
while (a[++i]<x&&i<h);
while(a[--j]>x);
if (i<j){
temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}
a[l] = a[j];
a[j] = x;
return j;
}
void qsort(int *a, int l, int h){
if (l>=h)
return;
int q = partition(a, l, h);
qsort(a, l, q-1);
qsort(a, q+1, h);
}
int main(){
int a[9] = {9,8,7,6,5,4,3,2,1};
qsort(a,0,8);
for (int i=0; i<9; i++)
cout<<a[i]<<endl;
return 0;
}
[代码] 非递归算法
数据规模很大时，递归的算法很容易导致栈溢出，改为非递归，模拟栈操作，最大长度为n，每次压栈时先压长度较大的，此时栈深度为logn。
#include <iostream>
using namespace std;
int partition(int *a, int l, int h){
int x = a[l];
int i = l;
int j = h+1;
int temp;
while (i<j){
while (a[++i]<x&&i<h);
while(a[--j]>x);
if (i<j){
temp = a[i];
a[i] = a[j];
a[j] = temp;
}
}
a[l] = a[j];
a[j] = x;
return j;
}
void qsort(int *a, int l, int h){
if (l>=h)
return;
int *s = new int[h-l+1];
int p = 0;
s[p++] = l;
s[p++] = h;
int low,high,q;
while (p>0){
high = s[--p];
low = s[--p];
if (low>=high)
break;
q = partition(a, low, high);
if (q-low > high-q){
s[p++] = low;
s[p++] = q-1;
if (high > q){
s[p++] = q+1;
s[p++] = high;
}
}else {
s[p++] = q+1;
s[p++] = high;
if (q > low){
s[p++] = low;
s[p++] = q-1;
}
}
}
delete []s;
}
int main(){
int a[9] = {9,8,7,6,5,4,3,2,1};
qsort(a,0,8);
for (int i=0; i<9; i++)
cout<<a[i]<<endl;
return 0;
}