题目链接：http://acm.nyist.edu.cn/JudgeOnline/problem.php?pid=32
求n个数中挑出r个数字的所有情况，最后倒序输出所有情况。
状压枚举所有情况就是了，判断长度是否符合条件。
1 /* 2 ━━━━━┒ギリギリ♂ eye！ 3 ┓┏┓┏┓┃キリキリ♂ mind！ 4 ┛┗┛┗┛┃＼○／ 5 ┓┏┓┏┓┃ / 6 ┛┗┛┗┛┃ノ) 7 ┓┏┓┏┓┃ 8 ┛┗┛┗┛┃ 9 ┓┏┓┏┓┃ 10 ┛┗┛┗┛┃ 11 ┓┏┓┏┓┃ 12 ┛┗┛┗┛┃ 13 ┓┏┓┏┓┃ 14 ┃┃┃┃┃┃ 15 ┻┻┻┻┻┻ 16 */ 17 #include <algorithm> 18 #include <iostream> 19 #include <iomanip> 20 #include <cstring> 21 #include <climits> 22 #include <complex> 23 #include <fstream> 24 #include <cassert> 25 #include <cstdio> 26 #include <bitset> 27 #include <vector> 28 #include <deque> 29 #include <queue> 30 #include <stack> 31 #include <ctime> 32 #include <set> 33 #include <map> 34 #include <cmath> 35 using namespace std; 36 #define fr first 37 #define sc second 38 #define cl clear 39 #define BUG puts("here!!!") 40 #define W(a) while(a--) 41 #define pb(a) push_back(a) 42 #define Rint(a) scanf("%d", &a) 43 #define Rll(a) scanf("%I64d", &a) 44 #define Rs(a) scanf("%s", a) 45 #define Cin(a) cin >> a 46 #define FRead() freopen("in", "r", stdin) 47 #define FWrite() freopen("out", "w", stdout) 48 #define Rep(i, len) for(LL i = 0; i < (len); i++) 49 #define For(i, a, len) for(LL i = (a); i < (len); i++) 50 #define Cls(a) memset((a), 0, sizeof(a)) 51 #define Clr(a, x) memset((a), (x), sizeof(a)) 52 #define Fuint(a) memset((a), 0x7f7f, sizeof(a)) 53 #define lrt rt << 1 54 #define rrt rt << 1 | 1 55 #define pi 3.14159265359 56 #define RT return 57 #define lowbit(x) x & (-x) 58 #define onenum(x) __builtin_popcount(x) 59 typedef long long LL; 60 typedef long double LD; 61 typedef unsigned long long Uint; 62 typedef pair<LL, LL> pii; 63 typedef pair<string, LL> psi; 64 typedef map<string, LL> msi; 65 typedef vector<LL> vi; 66 typedef vector<LL> vl; 67 typedef vector<vl> vvl; 68 typedef vector<bool> vb; 69 70 const int maxn = 15; 71 72 int a[maxn]; 73 int t[maxn]; 74 int n, r, cnt; 75 vector<vi> v; 76 77 int main() { 78 // FRead(); 79 Rep(i, maxn+1) a[i] = i + 1; 80 while(~scanf("%d%d", &n, &r)) { 81 int nn = 1 << n; 82 vi p; v.cl(); 83 For(i, 1, nn) { 84 cnt = 0; 85 Rep(j, n) { 86 if(i & (1 << j)) t[cnt++] = a[j]; 87 } 88 if(cnt == r) { 89 p.cl(); 90 for(int j = cnt - 1; j >= 0; j--) p.pb(t[j]); 91 v.pb(p); 92 } 93 } 94 sort(v.begin(), v.end()); 95 for(int i = v.size() - 1; i >= 0; i--) { 96 Rep(j, r) { 97 printf("%d", v[i][j]); 98 } 99 printf(" "); 100 } 101 } 102 RT 0; 103 }