Search in Rotated Sorted Array in Python

Consider we have an array sorted in ascending order, and that is rotated at some pivot unknown to you beforehand. For example, [0,1,2,4,5,6,7] might become [4,5,6,7,0,1,2]. We have given a target value to the search. If we can get it in the array, then return its index, otherwise return -1. We can assume no duplicate exists in the array. So if the array is like [4,5,6,7,0,1,2], then the output will be 4. as the index of this element is present at index 4.

To solve this, we will follow these steps −

• low := 0 and high := length of array
• while low < high
  • find mid as mid := low + (high - low)/2
  • if arr[mid] = target, then return mid
  • if arr[low] <= arr[mid]
    • if target >= arr[low] and target < arr[mid], then high := mid, otherwise low := mid + 1
  • otherwise
    • if target <= arr[high - 1] and target > arr[mid], then low := mid + 1, otherwise high := mid
• return -1

Example(Python)

Let us see the following implementation to get better understanding −

 Live Demo

class Solution(object):
   def search(self, nums, target):
      low = 0
      high = len(nums)
      while low<high:
         mid = low + (high-low)//2
         if nums[mid] == target:
            return mid
         if nums[low]<=nums[mid]:
            if target >=nums[low] and target <nums[mid]:
               high = mid
            else:
               low = mid+1
         else:
            if target<=nums[high-1] and target>nums[mid]:
               low = mid+1
            else:
               high = mid
      return -1
ob1 = Solution()
print(ob1.search([4,5,6,7,8,0,1,2], 0))

Input

[4,5,6,7,0,1,2]
0

Output

5

Arnab Chakraborty

Updated on: 27-Apr-2020

718 Views

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