67 Add Binary

链接：https://leetcode.com/problems/add-binary/
问题描述：
Given two binary strings, return their sum (also a binary string).

For example,
a = “11”
b = “1”
Return “100”.

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求两个二进制数字的相加。

class Solution {
public:
    string addBinary(string a, string b) {
        string result="";
        int flag=0;
        int num;
        int i=0;
        reverse(a.begin(),a.end());
        reverse(b.begin(),b.end());
        for(;i<a.length()&&i<b.length();i++)
        {
           num=a[i]-‘0‘+b[i]-‘0‘+flag;
           flag=num/2;
           num%=2;
           result+=num+‘0‘;
        }
        for(;i<a.length();i++)
        {
          num=a[i]-‘0‘+flag;
          flag=num/2;
           num%=2;
           result+=num+‘0‘;
        }
        for(;i<b.length();i++)
        {
          num=b[i]-‘0‘+flag;
          flag=num/2;
          num%=2;
          result+=num+‘0‘;
        }
        if(flag==1)
           result+=‘1‘;
        reverse(result.begin(),result.end());
        return result;
    }
};