solution.cpp

#include <bits/stdc++.h>
using namespace std;
class Solution
{
public:
	string addBinary(string a, string b)
	{
		string res;
		int carry = 0;
		int i = a.length() - 1;
		int j = b.length() - 1;
		for (; i >= 0 && j >= 0; i--, j--)
		{
			if (a[i] == '1' && b[j] == '1')
			{
				if (carry > 0)
				{
					res.push_back('1');
				}
				else
				{
					res.push_back('0');
				}
				carry = 1;
			}
			else if (a[i] == '0' && b[j] == '0')
			{
				if (carry > 0)
				{
					res.push_back('1');
				}
				else
				{
					res.push_back('0');
				}
				carry = 0;
			}
			else
			{
				if (carry > 0)
				{
					res.push_back('0');
					carry = 1;
				}
				else
				{
					res.push_back('1');
					carry = 0;
				}
			}
		}
		while (i >= 0)
		{
			if (a[i--] == '1')
			{
				if (carry > 0)
				{
					res.push_back('0');
					carry = 1;
				}
				else
				{
					res.push_back('1');
					carry = 0;
				}
			}
			else
			{
				res.push_back(carry + '0');
				carry = 0;
			}
		}
		while (j >= 0)
		{
			if (b[j--] == '1')
			{
				if (carry > 0)
				{
					res.push_back('0');
					carry = 1;
				}
				else
				{
					res.push_back('1');
					carry = 0;
				}
			}
			else
			{
				res.push_back(carry + '0');
				carry = 0;
			}
		}
		if (carry > 0)
		{
			res.push_back('1');
		}
		reverse(res.begin(), res.end());
		return res;
	}
};