Understanding Binary Search: A Step-by-Step Guide


Binary Search is a fundamental algorithm in computer science, widely used due to its efficiency in finding elements in a sorted array. Unlike linear search, which checks each element sequentially, binary search divides the search interval in half repeatedly, significantly reducing the number of comparisons. This post will explain the concept of binary search, provide a step-by-step breakdown of the algorithm, and offer implementation examples in various programming languages.

What is Binary Search?

Binary Search is a searching algorithm used to find the position of a target value within a sorted array. The algorithm works by repeatedly dividing the search interval in half. If the value of the search key is less than the item in the middle of the interval, the search continues in the lower half, or if it’s greater, the search continues in the upper half. This process continues until the value is found or the interval is empty.

How Binary Search Works: Step-by-Step

  1. Initialization:

    • Start with two pointers, low and high, pointing to the first and last index of the array, respectively.

  2. Calculate Middle:

    • Find the middle element of the current interval using the formula:
    • mid=low+(high−low)2mid=low+2(high−low)​

  3. Comparison:

    • Compare the target value with the middle element:

      • If they are equal, the target value is found.
      • If the target value is less than the middle element, repeat the process for the left half.
      • If the target value is greater than the middle element, repeat the process for the right half.

  4. Repeat:

    • Continue the process until the low pointer exceeds the high pointer, indicating that the target value is not present in the array.

Example Implementation in Python

def binary_search(arr, target):
    low = 0
    high = len(arr) - 1

    while low <= high:
        mid = low + (high - low) // 2

        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            low = mid + 1
            high = mid - 1

    return -1

# Example usage
arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
target = 7
result = binary_search(arr, target)
print("Element found at index:", result)

Analysis of Binary Search

  • Time Complexity:

    • The time complexity of binary search is 𝑂(log⁡𝑛)O(logn), where 𝑛n is the number of elements in the array. This is because the algorithm divides the search interval in half each time, leading to a logarithmic growth rate.

  • Space Complexity:

    • The space complexity of binary search is 𝑂(1)O(1) for the iterative approach and 𝑂(log⁡𝑛)O(logn) for the recursive approach due to the function call stack.

Common Applications of Binary Search

  1. Finding an Element in a Sorted Array:

    • The most common use of binary search is to find an element in a sorted array efficiently.

  2. Search in a Rotated Sorted Array:

    • Binary search can be modified to search for an element in a rotated sorted array.

  3. Finding the First or Last Occurrence of an Element:

    • Binary search can be adapted to find the first or last occurrence of a given element in a sorted array.

  4. Finding the Square Root of a Number:

    • Binary search can be used to find the square root of a number by searching within a range.


Binary Search is a powerful algorithm that provides an efficient way to search for elements in a sorted array. Understanding how it works and being able to implement it in various programming languages is a valuable skill for any programmer. By mastering binary search, you can improve the performance of your search operations and gain deeper insights into algorithm design and analysis.

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