67. Add Binary

1. 问题描述

Given two binary strings, return their sum (also a binary string).

For example,
a = "11"
b = "1"
Return "100".

Tags: Math String

2. 解答思路

3. 代码

#include <stack>
#include <string>
#include <cctype>
using namespace std;
class Solution {
public:
    string addBinary(string a, string b){
        int aLen = a.size();
        int bLen = b.size();
        if (0 == aLen)
        {
            return b;
        }
        if (0 == bLen)
        {
            return a;
        }

        if (aLen >= bLen)
        {
            return add(a, b);
        }
        else
        {
            return add(b, a);
        }
    }
private:
    string add(string a, string b)
    {
        int nTakeOver = 0;
        int i = b.size()-1;
        int j = a.size() - 1;
        std::string sum = "";
        std::string str_0 = "0";
        std::string str_1 = "1";

        for (; i>=0; i--,j--)
        {
            int ta = a[j] - '0';
            char tb = b[i] - '0';
            int r = (ta + tb + nTakeOver) % 2;
            nTakeOver = (ta + tb + nTakeOver) / 2;
            if (r == 0)
            {
                sum.insert(sum.begin(), str_0.begin(), str_0.end());
            }
            else
            {                    
                sum.insert(sum.begin(), str_1.begin(), str_1.end());
            }
        }
        if (j<0)
        {
            if (nTakeOver == 0)
            {
                return sum;
            }
            else
            {
                sum.insert(sum.begin(), str_1.begin(), str_1.end());
                return sum;
            }
        }
        else
        {
            while (j>=0)
            {
                int ta = a[j] - '0';
                int r = (ta + nTakeOver) % 2;
                nTakeOver = (ta + nTakeOver) / 2;
                if (r == 0)
                {
                    sum.insert(sum.begin(), str_0.begin(), str_0.end());
                }
                else
                {                    
                    sum.insert(sum.begin(), str_1.begin(), str_1.end());
                }
                j--;
            }
            if (nTakeOver == 0)
            {
                return sum;
            }
            else
            {
                sum.insert(sum.begin(), str_1.begin(), str_1.end());
                return sum;
            }
        }
    }
};

4. 反思