C++：数组排列组合的问题。

//求一个长度为n的数组中长度为m的所有排列组合。
#include <iostream>
#include <stack>
using namespace std;
stack<int> st;
void Grial(int a[], int m,int n, int length)
{
if (st.size() == 3)
{
stack<int> temp = st;
while (temp.empty() == false)
{
cout << temp.top() << " ";
temp.pop();
}
cout << endl;
return;
}
else
{
for (int i = m; i < n; i++)
{
st.push(a[i]);
Grial(a, i+1,n, length);
st.pop();
}
}
}
int main()
{
int a[] = {1,2,3,4,5,6,7};
Grial(a,0, sizeof(a) / sizeof(int), 3);
}*/
//求一个数组的全排列,代码情况如下：

#include <iostream>
using namespace std;
void Grial(int a[], int n,int m)
{
if (n == m)
{
for (int i = 0; i < m; i++)
{
cout << a[i] << " ";
}
cout << endl;
}
else
{
for (int i = n; i < m; i++)
{
std::swap(a[i],a
);
Grial(a,n+1,m);
std::swap(a[i],a
);
}
}
}
int main()
{
int a[] = { 1, 2, 3, 4 };
Grial(a, 0,sizeof(a) / sizeof(int));
return 0;
}