題目地址：https://leetcode-cn.com/problems/search-in-rotated-sorted-array/
思路：看複雜度知演算法，二分解決。區間要分清就可以了。
AC程式碼：

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