Problem

Given a sorted array of integers and a target value, find the index of the target value in the array. If the target value is not present in the array, return -1.
Example input: [1, 2, 3, 4, 5], 4
Example output: 3

Solution

def find_index(array, target):
    # Binary search is the optimal solution for this problem.
    # It is optimal because it is O(log n) time complexity.
    # This is because the array is sorted and we can use the
    # divide and conquer approach to find the target value.
    # We can do this by finding the midpoint of the array and
    # comparing the target value to the midpoint. If the target
    # value is less than the midpoint, we can search the left
    # half of the array. If the target value is greater than
    # the midpoint, we can search the right half of the array.
    # We can repeat this process until we find the target value.
    # If we do not find the target value, we can return -1.
    left = 0
    right = len(array) - 1
    while left <= right:
        mid = (left + right) // 2
        if array[mid] == target:
            return mid
        elif array[mid] < target:
            left = mid + 1
        else:
            right = mid - 1
    return -1

print(find_index([1, 2, 3, 4, 5], 4))
print(find_index([1, 2, 3, 4, 5], 6))