Search in Rotated Sorted Array

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.

Solution

the core idea is to find the target in already sorted part.

{% codeblock [lang:C++] %}

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

{% endcodeblock %}

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