Lintcode 62. Search in Rotated Sorted Array (Medium) (Python)

最新推荐文章于 2020-06-13 23:02:57 发布

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最新推荐文章于 2020-06-13 23:02:57 发布

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分类专栏： Lintcode刷题文章标签： Lintcode Python

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本文讨论了如何在已排序数组经过未知位移后进行目标值搜索的算法，提供了一个时间复杂度为O(logN)的解决方案。

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Search in Rotated Sorted Array

Description:

Suppose a sorted array 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.

Example
For [4, 5, 1, 2, 3] and target=1, return 2.

For [4, 5, 1, 2, 3] and target=0, return -1.

Challenge
O(logN) time

Code:

class Solution:
    """
    @param A: an integer rotated sorted array
    @param target: an integer to be searched
    @return: an integer
    """
    def search(self, A, target):
        # write your code here
        left, right = 0, len(A)-1
        while left <= right:
            mid = int((left+right)/2)
            if target == A[mid]:
                return mid

            if A[mid] >= A[left]:
                if target < A[mid] and target >= A[left]:
                    right = mid - 1
                else:
                    left = mid + 1

            elif A[mid] < A[left]:
                if target > A[mid] and target <= A[right]:
                    left = mid+1
                else:
                    right = mid-1

        return -1