https://oj.leetcode.com/problems/4sum/
find_minimum_in_rotated_sorted_array
https://oj.leetcode.com/problems/find-minimum-in-rotated-sorted-array/
https://oj.leetcode.com/problems/search-insert-position/
https://oj.leetcode.com/problems/search-insert-position/
solve 2 binary search problems