1.（排列数）输入两个正整数 $n, m (1 \leq n \leq 20, 1 \leq m \leq n)$，在 $1\sim n$ 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

1#include <iostream>2#include <cstring>3using namespace std;4const int	SIZE = 25;5bool		used[SIZE];6int		data[SIZE];7int		n, m, i, j, k;8bool		flag;9int main()10{11	cin >> n >> m;12	memset( used, false, sizeof(used) );13	for ( i = 1; i <= m; i++ )14	{15		data[i] = i;16		used[i] = true;17	}18	flag = true;19	while ( flag )20	{21		for ( i = 1; i <= m - 1; i++ )22			cout << data[i] << " ";23		cout << data[m] << endl;24		flag = ①;25		for ( i = m; i >= 1; i-- )26		{27			②;28			for ( j = data[i] + 1; j <= n; j++ )29				if ( !used[j] )30				{31					used[j] = true;32					data[i] = ③;33					flag	= true;34					break;35				}36			if ( flag )37			{38				for ( k = i + 1; k <= m; k++ )39					for ( j = 1; j <= ④; j++ )40						if ( !used[j] )41						{42							data[k] = j;43							used[j] = true;44							break;45						}46				⑤;47			}48		}49	}50}