Merge Sort

The merge sort is a recursive sort of order n*log(n).

It is notable for having a worst case and average complexity of O(n*log(n)), and a best case complexity of O(n) (for pre-sorted input). The basic idea is to split the collection into smaller groups by halving it until the groups only have one element or no elements (which are both entirely sorted groups). Then merge the groups back together so that their elements are in order. This is how the algorithm gets its “divide and conquer” description.

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First Bad Version

Problem description

The code base version is an integer start from 1 to n. One day, someone committed a bad version in the code case, so it caused this version and the following versions are all failed in the unit tests. Find the first bad version.

You can call isBadVersion to help you determine which version is the first bad one. The details interface can be found in the code’s annotation part.

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Binary Search Problem

For a given sorted array (ascending order) and a target number, find the first index of this number in O(log n) time complexity.

If the target number does not exist in the array, return -1.


If the array is [1, 2, 3, 3, 4, 5, 10], for given target 3, return 2.


If the count of numbers is bigger than 2^32, can your code work properly?
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