LeetCode:Search in Rotated Sorted Array

Problem：

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.

 

二分查找变形

 

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