[Leetcode]Rotated Sorted Array问题

LeetCode上牵扯到Rotated Sorted Array问题一共有四题，主要是求旋转数组的固定值或者最小值，都是考察二分查找的相关知识。在做二分查找有关的题目时，需要特别注重边界条件和跳出条件。在做题的过程中，不妨多设几个测试案例，自己判断一下。

下面是这四题的具体解答。

33.Search in Rotated Sorted Array

在求旋转数组中查找固定值，数组中每个数唯一出现。返回查找索引。

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

81.Search in Rotated Sorted Array II

在求旋转数组中查找固定值，数组中可能出现重复值。返回True或者False

class Solution(object):
    def search(self, nums, target):
        if not nums:
            return False
        low, high = 0, len(nums) - 1
        while low <= high:
            mid = low+(high-low) // 2
            if target == nums[mid]:
                return True
            if nums[low] < nums[mid]:
                if nums[low] <= target <= nums[mid]:
                    high = mid - 1
                else:
                    low = mid + 1
            elif nums[mid]<nums[low]:
                if nums[mid] <= target <= nums[high]:
                    low = mid + 1
                else:
                    high = mid - 1
            else:
                low+=1
        return False

153.Find Minimum in Rotated Sorted Array

在求旋转数组中查找最小值，数组中每个数唯一出现。返回最小值。

class Solution:
    def findMin(self, nums: List[int]) -> int:
        lo,hi = 0,len(nums)-1
        if nums[lo] < nums[hi]:return nums[lo] # 递增
        while hi-lo > 1:
            mid = lo+(hi-lo)//2
            if nums[lo] > nums[mid]:
                hi = mid
            elif nums[hi] < nums[mid]:
                lo = mid
        return nums[hi]

154.Find Minimum in Rotated Sorted Array II

在求旋转数组中查找最小值，数组中可能出现重复值。返回最小值。

class Solution:
    def findMin(self, nums: List[int]) -> int:
        if not nums:return
        lo,hi = 0,len(nums)-1
        if nums[lo] < nums[hi]:return nums[lo] # 递增
        minVal = nums[lo]
        while hi-lo>1:
            mid = lo+(hi-lo)//2
            if nums[lo] > nums[mid]:
                hi = mid
            elif nums[hi] < nums[mid]:
                lo = mid
            elif nums[mid] == nums[lo] == nums[hi]:
                for i in range(lo,hi):
                    if nums[i] < minVal:
                        minVal = nums[i]
                        hi = i
                return minVal
        return nums[hi]