（排列数）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

#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; } } } }