Python Program for Binary Search( Iterative method)

 

In  this search algorithm takes advantage of a collection of elements that is already sorted by ignoring half of the elements after just one comparison. 

1. Compare x with the middle element.
2. If x matches with the middle element, we return the mid index.
3. Else if x is greater than the mid element, then x can only lie in the right (greater) half subarray after the mid element. Then we apply the algorithm again for the right half.
4. Else if x is smaller, the target x must lie in the left (lower) half. So we apply the algorithm for the left half.

# Iterative Binary Search Function

# It returns index of x in given array arr if present,

# else returns -1

def binary_search(arr, x):

    low = 0

    high = len(arr) - 1

    mid = 0

 

    while low <= high:

 

        mid = (high + low) // 2

 

        # If x is greater, ignore left half

        if arr[mid] < x:

            low = mid + 1

 

        # If x is smaller, ignore right half

        elif arr[mid] > x:

            high = mid - 1

 

        # means x is present at mid

        else:

            return mid

 

    # If we reach here, then the element was not present

    return -1

 

 

# Test array

arr = [ 2, 3, 4, 10, 40 ]

x = 10

 

# Function call

result = binary_search(arr, x)

 

if result != -1:

    print("Element is present at index", str(result))

else:

    print("Element is not present in array")