33. Search in Rotated Sorted Array
https://leetcode.com/problems/search-in-rotated-sorted-array/discuss/
341. Flatten Nested List Iterator
- generator, sepecific to this question
- stack, interative https://leetcode.com/problems/flatten-nested-list-iterator/discuss/
155. Min Stack
https://discuss.leetcode.com/topic/7020/java-accepted-solution-using-one-stack