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.

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Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9Output: 4Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2Output: -1Explanation: 2 does not exist in nums so return -1

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Constraints:

• 1 <= nums.length <= 104

• -104?< nums[i], target < 104

• All the integers in?nums?are?unique.

• nums?is sorted in ascending order.

典型的二分法：