CSHARP

c# binary search

int BinarySearch(int[] nums, int target)
{
  if(nums == null || nums.Length == 0)
    return -1;

  int left = 0, right = nums.Length - 1;
  while(left <= right)
  {
    // Prevent (left + right) overflow
    int mid = left + (right - left) / 2;
    if(nums[mid] == target)
    { 
      return mid; 
    }
    else if(nums[mid] < target) 
    { 
      left = mid + 1; 
    }
    else 
    { 
      right = mid - 1; 
    }
  }
  // End Condition: left > right
  return -1;
}

c# binary search

// C# implementation of recursive Binary Search
using System;
  
class GFG {
    // Returns index of x if it is present in
    // arr[l..r], else return -1
    static int binarySearch(int[] arr, int l, int r, int x)
    {
        if (r >= l) {
            int mid = l + (r - l) / 2;
  
            // If the 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
            if (arr[mid] > x)
                return binarySearch(arr, l, mid - 1, x);
  
            // Else the element can only be present
            // in right subarray
            return binarySearch(arr, mid + 1, r, x);
        }
  
        // We reach here when element is not present
        // in array
        return -1;
    }
  
    // Driver method to test above
    public static void Main()
    {
  
        int[] arr = { 2, 3, 4, 10, 40 };
        int n = arr.Length;
        int x = 10;
  
        int result = binarySearch(arr, 0, n - 1, x);
  
        if (result == -1)
            Console.WriteLine("Element not present");
        else
            Console.WriteLine("Element found at index "
                              + result);
    }
}
  
// This code is contributed by Sam007.

generic binary search c#

using System;
					
public class Program
{
	public static void Main()
	{
		int[] arr = new int[] {1, 2, 3, 4, 4, 5, 6, 7, 7, 7, 7, 8};
		int query = 7;
		Console.WriteLine(Find(arr, query));
		Console.WriteLine(FindLeft(arr, query));
		Console.WriteLine(FindRight(arr, query));
	}
	public delegate string Condition(int mid);
    public static int GenericBinarySearch(int lo, int hi, Condition cond)
	{
		while(lo<=hi)
		{ 
			int mid = (lo+hi)/2;
			string result = cond(mid);
			if(result=="found") return mid;
			else if(result=="left") hi = mid-1;
			else lo=mid+1;
		}
		return -1;
	}
	public static int Find(int[] arr, int query)
	{
		int lo = 0;
		int hi = arr.Length-1;
		string CondLeft(int mid)
		{
			if(arr[mid]==query)
			{
				return "found";
			}
			else if(arr[mid]>query) 
			{
				return "left";
			}
			else return "right";
		}
		return GenericBinarySearch(lo, hi, CondLeft);
	}
	public static int FindLeft(int[] arr, int query)
	{
		int lo = 0;
		int hi = arr.Length-1;
		string CondLeft(int mid)
		{
			if(arr[mid]==query)
			{
				if(mid-1>0 && arr[mid-1]==query) return "left";
				return "found";
			}
			else if(arr[mid]>query) 
			{
				return "left";
			}
			else return "right";
		}
		return GenericBinarySearch(lo, hi, CondLeft);
	}
	public static int FindRight(int[] arr, int query)
	{
		int lo = 0;
		int hi = arr.Length-1;
		string CondLeft(int mid)
		{
			if(arr[mid]==query)
			{
				if(mid+1<arr.Length && arr[mid+1]==query) return "right";
				return "found";
			}
			else if(arr[mid]>query) 
			{
				return "left";
			}
			else return "right";
		}
		return GenericBinarySearch(lo, hi, CondLeft);
	}
}