Description

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

(i.e., [0,1,2,4,5,6,7] might become [4,5,6,7,0,1,2]).

You are given a target value to search. If found in the array return its index, otherwise return -1.

You may assume no duplicate exists in the array.

Your algorithm's runtime complexity must be in the order of O(log n).

Solution

二分法，分情況處理
（類似題目：找min）

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        if len(nums)==0:
            return -1
        start = 0
        end = len(nums)-1
        
        while start+1<end:
            mid = (start+end)//2
            if nums[mid]>nums[start]:
                if target >= nums[start] and target <=nums[mid]: 
                    end = mid
                else:
                    start = mid
            else:
                if target <= nums[end] and target >=nums[mid]: 
                    start = mid 
                else:
                    end = mid
        if target == nums[start]:
            return start
        if target == nums[end]:
            return end
        
        return -1