leetcode_question_67 Add Binary

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

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

 

bool isAllZero(string a)

{

    for (int i = 0; i < a.length(); ++i) {

        if (a[i] != '0')return false;

    }

    return true;

}

string stringxor(string a, string b) {

    string res="";

    int al = a.length()-1;

    int bl = b.length()-1;

    for (;al >=0 && bl >= 0; al--,bl--) {

        char tmp = '0' + (a[al]-'0')^(b[bl]-'0');

        res = tmp + res;

    }

    if (al >= 0) res = a.substr(0,al+1) + res;

    if (bl >= 0) res = b.substr(0,bl+1) + res;

    return res;

}



string stringand(string a, string b) {

    string res="";

    int al = a.length()-1;

    int bl = b.length()-1;

    for (;al >=0 && bl >= 0; al--,bl--) {

        char tmp = '0' + ((a[al]-'0')&(b[bl]-'0'));

        res = tmp + res;

    }

    return res;

}



string addBinary(string a, string b) {

    // Start typing your C/C++ solution below

    // DO NOT write int main() function

    if (a == "") return b;

    if (b == "") return a;



    string xorres = "";

    string andres = "";

    do {

        xorres = stringxor(a,b);

        andres = stringand(a,b);

        andres += '0';

        a = xorres;

        b = andres;

    } while (!isAllZero(b));



    int i = 0;

    for (; i < a.length(); ++i)

        if (a[i] != '0') break;

    if (i >= a.length())

        a = "0";

    else

        a = a.substr(i);

    return a;



}