Binary Search Program

2025-11-04 binary search searching algorithm sorted array search divide and conquer logical programs coding interview questions python binary search c binary search javascript search php binary search csharp binary search

Binary Search is an efficient algorithm to find an element in a sorted array by repeatedly dividing the search range. This guide includes explanation, algorithm steps, and code examples in Python, C, JavaScript, C#, and PHP.

Program Explanation

What is Binary Search?

Binary Search is an efficient searching algorithm used to find an element in a sorted array by repeatedly dividing the search interval into half. It works only on sorted data and has a time complexity of O(log n).

Steps to Solve

  1. Take a sorted array and the target element as input.
  2. Set two pointers: low = 0 and high = n - 1.
  3. Find the mid index using (low + high) // 2.
  4. If the mid element equals the target → element found.
  5. If the target is smaller → search in the left half.
  6. If the target is larger → search in the right half.
  7. Repeat until low exceeds high.

Key Points

  • Binary search works ONLY on a sorted list.
  • Much faster than linear search for large datasets.
  • Time Complexity: O(log n).
  • Frequently asked in coding interviews.

Program Code


arr = [2, 5, 8, 12, 16, 23, 38]
target = int(input("Enter number to search: "))

low, high = 0, len(arr) - 1

while low <= high:
    mid = (low + high) // 2
    
    if arr[mid] == target:
        print("Element found at index:", mid)
        break
    elif target < arr[mid]:
        high = mid - 1
    else:
        low = mid + 1
else:
    print("Element not found")
      

#include <stdio.h>

int main() {
    int arr[] = {2, 5, 8, 12, 16, 23, 38};
    int target, low = 0, high = 6, mid;

    printf("Enter number to search: ");
    scanf("%d", &target);

    while (low <= high) {
        mid = (low + high) / 2;

        if (arr[mid] == target) {
            printf("Element found at index: %d", mid);
            return 0;
        } 
        else if (target < arr[mid]) {
            high = mid - 1;
        } 
        else {
            low = mid + 1;
        }
    }

    printf("Element not found");
    return 0;
}
      

let arr = [2, 5, 8, 12, 16, 23, 38];
let target = Number(prompt("Enter number to search:"));

let low = 0, high = arr.length - 1;

while (low <= high) {
    let mid = Math.floor((low + high) / 2);

    if (arr[mid] === target) {
        console.log("Element found at index:", mid);
        break;
    } else if (target < arr[mid]) {
        high = mid - 1;
    } else {
        low = mid + 1;
    }
}

if (low > high) console.log("Element not found");
      

using System;

class Program {
    static void Main() {
        int[] arr = {2, 5, 8, 12, 16, 23, 38};
        Console.Write("Enter number to search: ");
        int target = int.Parse(Console.ReadLine());

        int low = 0, high = arr.Length - 1;

        while (low <= high) {
            int mid = (low + high) / 2;

            if (arr[mid] == target) {
                Console.WriteLine("Element found at index: " + mid);
                return;
            }
            else if (target < arr[mid]) {
                high = mid - 1;
            }
            else {
                low = mid + 1;
            }
        }

        Console.WriteLine("Element not found");
    }
}
      

<?php
$arr = [2, 5, 8, 12, 16, 23, 38];
$target = intval(readline("Enter number to search: "));

$low = 0;
$high = count($arr) - 1;

while ($low <= $high) {
    $mid = intdiv($low + $high, 2);

    if ($arr[$mid] == $target) {
        echo "Element found at index: $mid";
        exit;
    } elseif ($target < $arr[$mid]) {
        $high = $mid - 1;
    } else {
        $low = $mid + 1;
    }
}

echo "Element not found";
?>
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