leetcode

0 class Solution {

1 vector<string> res;

2 string crnt;

3

4 void rec(int n, int k, char last = 'x') {

5 if (res.size() == k) return;

6 if (crnt.size() == n) {

7 res.push_back(crnt);

8 return;

9 }

10 crnt.push_back(' ');

11 for (char c = 'a'; c <= 'c'; c++) {

12 if (c == last) continue;

13 crnt.back() = c;

14 rec(n, k, c);

15 }

16 crnt.pop_back();

17 }

18

19 public:

20 string getHappyString(int n, int k) {

21 if (k > 3 * (1 << n - 1)) return "";

22 rec(n, k);

23 return res.back();

24 }

25 };