题目描述
输入两个正整数 n,m(1≤n≤20,1≤m≤n)，在 1∼n 中任取 m 个数，按字典序从小到大输出所有这样的排列。
例如：
输入：3 2
输出：1 2
1 3
2 1
2 3
3 1
3 2
程序代码
#include <iostream>
#include <cstring>
using namespace std;
const int SIZE = 25;
bool used[SIZE];
int data[SIZE];
int n, m, i, j, k;
bool flag;
int main()
{
cin >> n >> m;
memset( used, false, sizeof(used) );
for ( i = 1; i <= m; i++ )
{
data[i] = i;
used[i] = true;
}
flag = true;
while ( flag )
{
for ( i = 1; i <= m - 1; i++ )
cout << data[i] << " ";
cout << data[m] << endl;
flag = ①;
for ( i = m; i >= 1; i-- )
{
②;
for ( j = data[i] + 1; j <= n; j++ )
if ( !used[j] )
{
used[j] = true;
data[i] = ③;
flag = true;
break;
}
if ( flag )
{
for ( k = i + 1; k <= m; k++ )
for ( j = 1; j <= ④; j++ )
if ( !used[j] )
{
data[k] = j;
used[j] = true;
break;
}
⑤;
}
}
}
}