LeetCode Add Binary

 1 class Solution {
 2 public:
 3     string addBinary(string a, string b) {
 4         string res;
 5         int carry = 0, s = 0;
 6         int apos = a.length() - 1;
 7         int bpos = b.length() - 1;
 8         int astp = 0, bstp = 0;
 9         // skip leading zero(s)
10         for (; astp < apos && a[astp] == ‘0‘; astp++);
11         for (; bstp < bpos && b[bstp] == ‘0‘; bstp++);
12         // a/b pos validation
13         bool apv = apos >= astp, bpv = bpos >= bstp;
14         // addition
15         while(apv || bpv) {
16             if (apv) s += a[apos] - ‘0‘;
17             if (bpv) s += b[bpos] - ‘0‘;
18             carry = s > 1;
19             s = s & 0x1;
20             res.push_back(s ? ‘1‘ : ‘0‘);
21             apos--, bpos--, s = carry;
22             apv = apos >= astp, bpv = bpos >= bstp;
23         }
24         if (carry) res.push_back(‘1‘);
25         if (res.empty()) {
26             res.push_back(‘0‘);
27         } else {
28             reverse(res.begin(), res.end());
29         }
30         return res;
31     }
32 };