Explain the working principle of the binary search algorithm and its main steps.

The binary search algorithm is used for quickly finding an element in a sorted array. Its principle is based on dividing the search area in half at each step.

Main steps:

1. Determine the middle of the current search range.
2. Compare the target element with the element in the middle.
3. If they are equal — the element is found.
4. If the target element is less than the middle, repeat the search in the left half.
5. If it is greater — in the right half.
6. Repeat until the range becomes empty.

Example in Python:

def binary_search(arr, target):
    left, right = 0, len(arr) - 1
    while left <= right:
        mid = (left + right) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            left = mid + 1
        else:
            right = mid - 1
    return -1  # element not found

# Usage
arr = [1, 3, 5, 7, 9]
print(binary_search(arr, 7))  # Outputs 3