[LeetCode] Add Binary

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) {
        int la = a.size(), lb = b.size();
        int len = max(la, lb) + 2;
        char* res = new char[len];
        memset(res, 0, len);
        int left = 0, cur;
        int ia = la - 1, ib = lb - 1, ic = len - 2;
        while (ia >= 0 && ib >= 0) {
            cur = a[ia--] + b[ib--] - 2 * '0' + left;
            if (cur > 1) {
                res[ic--] = '0' + cur % 2;
                left = 1;
            } else {
                res[ic--] = '0' + cur;
                left = 0;
            }
        }
        
        while (ia >= 0) {
            cur = a[ia--] - '0' + left;
            if (cur > 1) {
                res[ic--] = '0' + cur % 2;
                left = 1;
            } else {
                res[ic--] = '0' + cur;
                left = 0;
            }
        }
        while (ib >= 0) {
            cur = b[ib--] + left - '0';
            if (cur > 1) {
                res[ic--] = '0' + cur % 2;
                left = 1;
            } else {
                res[ic--] = '0' + cur;
                left = 0;
            }
        }
        if (left > 0) res[ic--] = '1';
        return string(res+ic+1);
        
    }
};