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 = , K =
O/p: 

题目：从N个数中选K个，输出所有选法。

解法：递归解决。

代码：

 // http://www.careercup.com/question?id=6204973461274624
 #include <vector>
 using namespace std;

 class Solution {
 public:
     void findKSubsets(int n, int k, vector<vector<int> > &result) {
         if (n <= ) {
             return;
         }
         if (k <  || k > n) {
             return;
         }

         vector<int> subset;

         DFS(, , subset, result, n, k);
     }
 private:
     void DFS(int in, int ik, vector<int> &subset,
              vector<vector<int> > &result,
              const int &n, const int &k) {
         if (ik == k) {
             result.push_back(subset);
             return;
         }

         int i;
         for (i = in + ; i <= n - (k - ik) + ; ++i) {
             subset.push_back(i);
             DFS(i, ik + , subset, result, n, k);
             subset.pop_back();
         }
     };
 };

 int main()
 {
     vector<vector<int> > result;
     int n, k;
     int i, j;
     Solution sol;

     while (scanf("%d%d", &n, &k) ==  && (n >  && k > )) {
         sol.findKSubsets(n, k, result);
         printf("{\n");
         for (i = ; i < (int)result.size(); ++i) {
             printf("    {");
             for (j = ; j < (int)result[i].size(); ++j) {
                 printf((j ? ", %d" : "%d"), result[i][j]);
             }
             printf("}\n");
         }
         printf("}\n");

         for (i = ; i < (int)result.size(); ++i) {
             result[i].clear();
         }
         result.clear();
     }

     return ;
 }