LeetCode算法题目: Search in Rotated Sorted Array

题目：

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.

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分析：

此题目难度为hard，解此题目采用二分查找.难度在于如何确定边界。

二分查找算法就是不断将数组进行对半分割，每次拿中间元素和目标值进行比较。时间复杂度为O（log(n)）

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代码实现：

class Solution { public: int search(vector<int>& nums, int target) { int first = 0, last = nums.size(); while (first != last) { const int mid = first + (last - first) / 2; if (nums[mid] == target) return mid; if (nums[first] <= nums[mid]) { if (nums[first] <= target && target < nums[mid]) last = mid; else first = mid + 1; } else { if (nums[mid] < target && target <= nums[last-1]) first = mid + 1; else last = mid; } } return -1; } };