Binary Search HW

HW Hack #1

def search_rotated_array(arr, target):
    left, right = 0, 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

print(search_rotated_array([4,5,6,7,0,1,2], 0))  

4

HW Hack #2

def find_first_and_last(arr, target):
    def find_bound(is_first):
        left, right = 0, len(arr) - 1
        result = -1

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

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

        return result

    first = find_bound(True)
    if first == -1:
        return -1

    last = find_bound(False)
    return (first, last)
print(find_first_and_last([1, 2, 2, 2, 3, 4, 5], 2))  

(1, 3)

HW Hack #3

def search_smallest_element(arr, target):
    left, right = 0, 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

print(search_smallest_element([1, 3, 5, 7, 9], 6))  

7