Python Program for Binary Search (Recursive and Iterative)
In a nutshell, this search algorithm takes advantage of a collection of elements that is already sorted by ignoring half of the elements after just one comparison.
- Compare x with the middle element.
- If x matches with the middle element, we return the mid index.
- 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.
- Else if x is smaller, the target x must lie in the left (lower) half. So we apply the algorithm for the left half.
Recursive :
# Python 3 program for recursive binary search. # Modifications needed for the older Python 2 are found in comments. # Returns index of x in arr if present, else -1 def binary_search(arr, low, high, x): # Check base case if high >= low: mid = (high + low) // 2 # If element is present at the middle itself if arr[mid] == x: return mid # If element is smaller than mid, then it can only # be present in left subarray elif arr[mid] > x: return binary_search(arr, low, mid - 1, x) # Else the element can only be present in right subarray else: return binary_search(arr, mid + 1, high, x) else: # Element is not present in the array return -1 # Test array arr = [ 2, 3, 4, 10, 40 ] x = 10 # Function call result = binary_search(arr, 0, len(arr)-1, x) if result != -1: print("Element is present at index", str(result)) else: print("Element is not present in array") |
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Output:
Element is present at index 3
Iterative:
# 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 # Check if x is present at mid if arr[mid] < x: low = mid + 1 # If x is greater, ignore left half elif arr[mid] > x: high = mid - 1 # If x is smaller, ignore right half 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") |
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Output:
Element is present at index 3
Please refer to the article Binary Search for more details!
