Binary Search

Given an array of integers `nums` which is sorted in ascending order, and an integer `target`, write a function to search `target` in `nums`. If `target` exists, then return its index. Otherwise, return `-1`. You must write an algorithm with `O(log n)` runtime complexity. **Example 1:** ``` Input: nums = [-1,0,3,5,9,12], target = 9 Output: 4 Explanation: 9 exists in nums and its index is 4. ``` **Example 2:** ``` Input: nums = [-1,0,3,5,9,12], target = 2 Output: -1 Explanation: 2 does not exist in nums so return -1. ``` **Example 3:** ``` Input: nums = [5], target = 5 Output: 0 ```