【LeetCode】67. Add Binary 解题小结

题目：

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

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

class Solution {
public:
    string addBinary(string a, string b) {
       string res(a.size()+b.size(),‘0‘);
       int i = a.size()-1;
       int j = b.size()-1;
       int k = res.size()-1;
       int carry = 0;

       while(i >= 0 || j >= 0 || carry){
           int sum = 0;
           if (i >= 0) sum += a[i--] - ‘0‘;
           if (j >= 0) sum += b[j--] - ‘0‘;
           if (carry) sum += carry;
           res[k--] = ‘0‘ + (sum%2);
           carry = sum / 2;
       }

        std::size_t pos = res.find_first_not_of(‘0‘);
        return pos == std::string::npos ? "0":res.substr(pos);
    }
};