题目
There is an integer array nums sorted in ascending order (with distinct values).
Prior to being passed to your function, nums is possibly rotated at an unknown pivot index k (1 <= k < nums.length) such that the resulting array is [nums[k], nums[k+1], ..., nums[n-1], nums[0], nums[1], ..., nums[k-1]] (0-indexed). For example, [0,1,2,4,5,6,7] might be rotated at pivot index 3 and become [4,5,6,7,0,1,2].
Given the array nums after the possible rotation and an integer target, return the index of target if it is in nums, or -1 if it is not in nums.
You must write an algorithm with O(log n) runtime complexity.
Example 1:
Input: nums = [4,5,6,7,0,1,2], target = 0
Output: 4
Example 2:
Input: nums = [4,5,6,7,0,1,2], target = 3
Output: -1
Example 3:
Input: nums = [1], target = 0
Output: -1
Constraints:
1 <= nums.length <= 5000-10^4 <= nums[i] <= 10^4- All values of
numsare unique. numsis an ascending array that is possibly rotated.-10^4 <= target <= 10^4
思路
两次二分查找，第一次查找数组反转的边界，将数组分隔为左右两个数组。在根据目标值的大小判断是使用左数组还是右数组后，再进行一次二分查找找出目标值的位置。
代码
python版本：
class Solution:
def search(self, nums: List[int], target: int) -> int:
l, r = 0, len(nums)
while l < r:
mid = (l+r)//2
if nums[mid] >= nums[0]:
l = mid+1
else:
r = mid
if target >= nums[0]:
l = 0
else:
r = len(nums)
while l < r:
mid = (l+r)//2
if nums[mid] > target:
r = mid
elif nums[mid] < target:
l = mid+1
else:
return mid
return -1
