#1286

Iterator for Combination

medium · 72.7% accepted · 1,390 likes · top 82%

string · backtracking · design · iterator

⊣ practice⊣ open on leetcode ↗

Description

Design the CombinationIterator class:

 - CombinationIterator(string characters, int combinationLength) Initializes the object with a string characters of sorted distinct lowercase English letters and a number combinationLength as arguments.

 - next() Returns the next combination of length combinationLength in lexicographical order.

 - hasNext() Returns true if and only if there exists a next combination.

Example 1:

Input
["CombinationIterator", "next", "hasNext", "next", "hasNext", "next", "hasNext"]
[["abc", 2], [], [], [], [], [], []]
Output
[null, "ab", true, "ac", true, "bc", false]

Example 2:

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

Solution