67. 二进制求和

67. 二进制求和

class Solution {
    public String addBinary(String a, String b) {
        Deque<Character> ansSeq = new LinkedList<>();
        int indexA = a.length() - 1;
        int indexB = b.length() - 1;
        int flag = 0;
        while (indexA >= 0 || indexB >= 0) {
            char cha = (indexA >= 0 ? a.charAt(indexA) : '0');
            char chb = (indexB >= 0 ? b.charAt(indexB) : '0');
            int sum = (cha - '0') + (chb - '0') + flag;
            if (sum == 0) {
                ansSeq.add('0');
                flag = 0;
            } else if (sum == 1) {
                ansSeq.add('1');
                flag = 0;
            } else if (sum == 2) {
                ansSeq.add('0');
                flag = 1;
            } else {
                ansSeq.add('1');
                flag = 1;
            }
            --indexA;
            --indexB;
        }
        if (flag == 1)
            ansSeq.add('1');
        StringBuilder ans = new StringBuilder();
        while (!ansSeq.isEmpty()) 
            ans.append(ansSeq.removeLast());
        return ans.toString();
    }
}