Add Binary

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) {
        if(a.size() == 0) return b;
        if(b.size() == 0) return a;
        string ret;
        int carry = 0;
        int i = a.size() - 1;
        int j = b.size() - 1;
        while(i>=0 && j>=0) {
            int tmp = a[i] - '0' + b[j] - '0' + carry;
            carry = tmp / 2;
            ret = (char)('0' + tmp%2) + ret;  
            --i;
            --j;
        }
        
        while(i>=0) {
            int tmp = a[i] - '0' + carry;
            carry = tmp/2;
            ret = (char)('0' + tmp%2) + ret;
            --i;
        }
        
        while(j>=0) {
            int tmp = b[j] - '0' + carry;
            carry = tmp/2;
            ret = (char)('0' + tmp%2) + ret;
            --j;
        }
        
        if(carry) ret = (char)('0' + carry) + ret;
        
        return ret;
    }
};

 

 

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