binarysearch

Hack 1

def binary_search_rotated(arr, target):
    left = 0
    right = len(arr) - 1

    while left <= right:
        mid = (left + right) // 2

        if arr[mid] == target:
            return mid

        if arr[left] <= arr[mid]:
            if arr[left] <= target < arr[mid]:
                right = mid - 1
            else:
                left = mid + 1
        else:
            if arr[mid] < target <= arr[right]:
                left = mid + 1
            else:
                right = mid - 1

    return -1

arr = [4, 5, 6, 7, 0, 1, 2]
target = 1
print(binary_search_rotated(arr, target))

5

Hack 2

def find_first_and_last(arr, target):
    left = 0
    right = len(arr) - 1
    first = -1
    while left <= right:
        mid = (left + right) // 2
        if arr[mid] == target:
            first = mid
            right = mid - 1
        elif arr[mid] < target:
            left = mid + 1
        else:
            right = mid - 1

    left = 0
    right = len(arr) - 1
    last = -1
    while left <= right:
        mid = (left + right) // 2
        if arr[mid] == target:
            last = mid
            left = mid + 1
        elif arr[mid] < target:
            left = mid + 1
        else:
            right = mid - 1

    if first == -1:
        return -1
    return (first, last)

arr = [1, 2, 2, 2, 3, 4, 5]
target = 2
print(find_first_and_last(arr, target))

(1, 3)

Hack 3

def search_smallest_greater_or_equal(arr, target):
    left = 0
    right = len(arr) - 1
    result = -1

    while left <= right:
        mid = (left + right) // 2
        if arr[mid] >= target:
            result = arr[mid]
            right = mid - 1
        else:
            left = mid + 1

    return result

arr = [1, 3, 5, 7, 9, 11]
target = 8
print(search_smallest_greater_or_equal(arr, target))

9