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mediumDSA

How do you search in a rotated sorted array?

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01

Understand the problem

Explain modified binary search.

binary-searcharrays
02

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Sketch your approach before reading the solution — that's what interviews test.

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03

Study the solution

Run binary search, but at each step decide which half is sorted by comparing nums[mid] to the ends. If the target lies within the sorted half's range, search there; otherwise search the other half. Still O(log n) despite the rotation.

Solution ready — 2 min read

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04

Read the code

Binary search on a rotated array
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def search(nums, target):
    lo, hi = 0, len(nums) - 1
    while lo <= hi:
        mid = (lo + hi) // 2
        if nums[mid] == target:
            return mid
        if nums[lo] <= nums[mid]:                 # left half sorted
            if nums[lo] <= target < nums[mid]:
                hi = mid - 1
            else:
                lo = mid + 1
        else:                                     # right half sorted
            if nums[mid] < target <= nums[hi]:
                lo = mid + 1
            else:
                hi = mid - 1
    return -1


# --- demo ---
print(search([4, 5, 6, 7, 0, 1, 2], 0))   # 4
print(search([4, 5, 6, 7, 0, 1, 2], 3))   # -1
05

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