leetcode

0 class Solution {

1 vector<int> vec;

2 const string chars;

3 string res;

4

5 bool has_next = true;

6 void shuffle() {

7 int goal = chars.size() - 1, idx = vec.size() - 1;

8 while (idx > 0 && vec[idx] == goal)

9 goal--, idx--;

10 for (int i = idx, acc = vec[idx]; i < vec.size(); i++)

11 res[i] = chars[vec[i] = ++acc];

12 if (idx == 0 && vec[0] == goal) has_next = false;

13 }

14

15 public:

16 CombinationIterator(string chars, int len) : chars(chars), vec(len), res(len, ' ') {

17 for (int i = 0; i < len; i++)

18 res[i] = chars[vec[i] = i];

19 vec.back()--;

20 }

21

22 string next() {

23 shuffle();

24 return res;

25 }

26

27 bool hasNext() { return has_next; }

28 };