1286. Iterator for Combination

Medium

30 Points

String

Backtracking

Design

Iterator

Design the CombinationIterator class:

Examples

Example 1

Input ["CombinationIterator", "next", "hasNext", "next", "hasNext", "next", "hasNext"] [["abc", 2], [], [], [], [], [], []] Output [null, "ab", true, "ac", true, "bc", false] Explanation CombinationIterator itr = new CombinationIterator("abc", 2); itr.next(); // return "ab" itr.hasNext(); // return True itr.next(); // return "ac" itr.hasNext(); // return True itr.next(); // return "bc" itr.hasNext(); // return False

Constraints

1 <= combinationLength <= characters.length <= 15
All the characters of characters are unique.
At most 104 calls will be made to next and hasNext.
It is guaranteed that all calls of the function next are valid.