LeetCode-67. Add Binary [C++][Java]

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Given two binary strings a and b, return their sum as a binary string.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

Constraints:

1 <= a.length, b.length <= 10^4a and b consist only of '0' or '1' characters.Each string does not contain leading zeros except for the zero itself.

class Solution {
public:
    string addBinary(string a, string b) {
        int i = a.length() - 1;
        int j = b.length() - 1;
        string ans;
        int carry = 0;
        while (i >= 0 || j >= 0 || carry){
            if (i >= 0) {
                carry += a[i] - '0';
                i--;
            }
            if (j >= 0) {
                carry += b[j] - '0';
                j--;
            }
            ans = (char)(carry % 2 + '0') + ans;
            carry = carry / 2;
        }
        return ans;
    }
};

class Solution {
    public String addBinary(String a, String b) {
        int i = a.length() - 1;
        int j = b.length() - 1;
        String ans = "";
        int carry = 0;
        while (i >= 0 || j >= 0 || carry > 0){
            if (i >= 0) {
                carry += a.charAt(i) - '0';
                i--;
            }
            if (j >= 0) {
                carry += b.charAt(j) - '0';
                j--;
            }
            ans = (char)(carry % 2 + '0') + ans;
            carry = carry / 2;
        }
        return ans;
    }
}