剑指 Offer II 002. 二进制加法 #

class Solution {
    public String addBinary(String a, String b) {
        String longer = a.length() > b.length() ? a : b, shorter = a.length() > b.length() ? b : a;
        int ptrLonger = longer.length() - 1, ptrShorter = shorter.length() - 1;
        char[] ans = longer.toCharArray();
        int sum = 0, carry = 0;
        while (ptrShorter >= 0) {
            sum = longer.charAt(ptrLonger) - '0' + shorter.charAt(ptrShorter) - '0' + carry;
            ans[ptrLonger] = sum % 2 > 0 ? '1' : '0';
            carry = sum > 1 ? 1 : 0;
            ptrLonger--; ptrShorter--;
        }
        while (carry > 0) {
            if (ptrLonger == -1) return "1" + String.valueOf(ans);
            sum = ans[ptrLonger] - '0' + carry;
            ans[ptrLonger--] = sum % 2 > 0 ? '1' : '0';
            carry = sum > 1 ? 1 : 0;
        }
        return String.valueOf(ans);
    }
}