算法描述：

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]).

Find the minimum element.

You may assume no duplicate exists in the array.

Example 1:

Input: [3,4,5,1,2] 
Output: 1

Example 2:

Input: [4,5,6,7,0,1,2]
Output: 0

解题思路：二分法，注意细节。

        if(nums.size()==1) return nums[0];
        int left = 0;
        int right = nums.size()-1;
        while(left < right){
            if(nums[left] < nums[right]) return nums[left];
            int mid = left + (right - left) / 2;
            if(nums[mid] > nums[right]){
                left = mid +1;
            } else
                right = mid;
        }
        return nums[left];
    }