Problem: Binary Addition

CSharp · Console

/Program.cs

using System;

public class Program
{
    /*
     *  Two binary numbers as strings, add the numbers together and return
     *  the result as a binary string.
     *
	 *    10 + 1 => 11
     *    1001 + 1 => 1010
	 *	  1101 + 100 => 10001
	 *    10101010 + 11001100 => 101110110
     */
	public static void Main()
	{
		Console.WriteLine(AddBinaryNumbers("10","1"));
		Console.WriteLine(AddBinaryNumbers("1001","1"));
		Console.WriteLine(AddBinaryNumbers("1101", "100"));
		Console.WriteLine(AddBinaryNumbers("10101010", "11001100"));
	}
	
	public static string AddBinaryNumbers(string a, string b)
	{
		string result = "";

		// Initialize digit sum 
		int s = 0;

		// Traverse both strings starting from last characters 
		int i = a.Length - 1;
		int j = b.Length - 1;

		// O(n) + O(n) -> O(2n)
		while (i >= 0 || j >= 0 || s == 1)
		{
			// Padding cases, so if there is '1' + '101' it actually will be '001' + '101'
			// Note: '1'-'0' converts char back to its numeric value
			s += (i >= 0 ? a[i] - '0' : 0); // Add character "a[i]" as a numeric value to s.
			s += (j >= 0 ? b[j] - '0' : 0); // Add character "b[i]" as a numeric value to s.

			// numeric + '0' converts it to corresponding char again
			// If current digit sum (s) is 1 or 3, add '1' to result, otherwise add a '0' char
			result = (char)(s % 2 + '0') + result;

			// Compute carry over.
			s /= 2;

			// Decrement our index. 
			i--; 
			j--;
		}
		return result;
	}
}