LeetCode/67. AddBinary

https://leetcode.com/problems/add-binary/

Summary

Given two binary strings and return their sum.

Solutions

My Solution

In my solution, the idea using two pointer was correct. However checking for the short and long string was a bit too much.

public string Solution(string a, string b)
{
    var shorterString = "";
    var longerString = "";
    int pointerS, pointerL = 0;
    var output = "";

    if (a.Length > b.Length)
    {
        shorterString = b;
        pointerS = b.Length - 1;
        longerString = a;
        pointerL = a.Length - 1;
    }
    else
    {
        shorterString = a;
        pointerS = a.Length - 1;
        longerString = b;
        pointerL = b.Length - 1;
    }

    var carry = 0;

    while (pointerS >= 0)
    {
        var l = Int32.Parse(shorterString[pointerS].ToString());
        var r = Int32.Parse(longerString[pointerL].ToString());
        var sum = l + r + carry;

        if (sum > 1)
        {
            sum = sum % 2;
            carry = 1;
        }
        else
        {
            carry = 0;
        }

        output = sum + output;
        pointerS--;
        pointerL--;
    }

    while (pointerL >= 0)
    {
        var r = Int32.Parse(longerString[pointerL].ToString());
        var sum = r + carry;

        if (sum > 1)
        {
            sum = sum % 2;
            carry = 1;
        }
        else
        {
            carry = 0;
        }

        output = sum + output;
        pointerL--;
    }

    output = carry == 1 ? "1" + output : output;

    return output;
}

Best Solution

In the best solution, we only check for the pointer is bigger than 0. And then move pointer to get a correct output.

public string BestSolution(string a, string b)
{
    int pointerA = a.Length - 1;
    int pointerB = b.Length - 1;
    var output = "";
    var carry = 0;

    while (pointerA >= 0 || pointerB >= 0)
    {
        var sum = carry;
        if (pointerA >= 0) sum += Int32.Parse(a[pointerA--].ToString());
        if (pointerB >= 0) sum += Int32.Parse(b[pointerB--].ToString());

        output = (sum % 2) + output;
        carry = sum / 2;
    }

    output = carry == 1 ? "1" + output : output;

    return output;
}
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