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.

Example

For [4, 5, 1, 2, 3] and target = 1, return 2.

For [4, 5, 1, 2, 3] and target = 0, return -1.

Solution

Binary search.

• A[low] < A[mid]: the left half is monotonically increasing, the "breaking point" is on the right
  • if the target falls in this left half, check left half
  • otherwise check right half
• A[low] > A[mid], or A[mid] < A[high]: the right half is monotonically increasing
  • if the target falls in the right half, check right half
  • otherwise check left half