Careercup - Facebook面试题 - 6204973461274624

2014-05-02 02:28

题目链接

原题：

I/P: N, k 



O/P: all subset of N with exactly K elements. 



eg: I/p: N = 5, K =3 

O/p: 



1 2 3 

1 2 4 

1 2 5 

1 3 4 

1 3 5 

2 3 4 

2 3 5 

3 4 5

题目：从N个数中选K个，输出所有选法。

解法：递归解决。

代码：

 1 // http://www.careercup.com/question?id=6204973461274624

 2 #include <vector>

 3 using namespace std;

 4 

 5 class Solution {

 6 public:

 7     void findKSubsets(int n, int k, vector<vector<int> > &result) {

 8         if (n <= 0) {

 9             return;

10         }

11         if (k < 1 || k > n) {

12             return;

13         }

14         

15         vector<int> subset;

16         

17         DFS(0, 0, subset, result, n, k);

18     }

19 private:

20     void DFS(int in, int ik, vector<int> &subset, 

21              vector<vector<int> > &result, 

22              const int &n, const int &k) {

23         if (ik == k) {

24             result.push_back(subset);

25             return;

26         }

27         

28         int i;

29         for (i = in + 1; i <= n - (k - ik) + 1; ++i) {

30             subset.push_back(i);

31             DFS(i, ik + 1, subset, result, n, k);

32             subset.pop_back();

33         }

34     };

35 };

36 

37 int main()

38 {

39     vector<vector<int> > result;

40     int n, k;

41     int i, j;

42     Solution sol;

43     

44     while (scanf("%d%d", &n, &k) == 2 && (n > 0 && k > 0)) {

45         sol.findKSubsets(n, k, result);

46         printf("{\n");

47         for (i = 0; i < (int)result.size(); ++i) {

48             printf("    {");

49             for (j = 0; j < (int)result[i].size(); ++j) {

50                 printf((j ? ", %d" : "%d"), result[i][j]);

51             }

52             printf("}\n");

53         }

54         printf("}\n");

55         

56         for (i = 0; i < (int)result.size(); ++i) {

57             result[i].clear();

58         }

59         result.clear();

60     }

61     

62     return 0;

63 }