67. Add Binary

摘要： Given two binary strings, return their sum (also a binary string). The input strings are both non-empty and contains only characters 1 or 0. Ex...

Given two binary strings, return their sum (also a binary string).

The input strings are both non-empty and contains only characters 1 or 0.

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

Example 2:
Input: a = "1010", b = "1011"
Output: "10101"

難度: easy

題目：

給定兩個二進位制字串，返回它們的和（也是二進位制字串）。

字串都不為空且只有0､1組成。

Runtime: 2 ms, faster than 95.70% of Java online submissions for Add Binary.

Memory Usage: 26.2 MB, less than 54.54% of Java online submissions for Add Binary.

public class Solution {
public String addBinary(String a, String b) {
int i = a.length() - 1, j = b.length() - 1, carry = 0;
StringBuilder result = new StringBuilder();
while (i >= 0 || j >= 0) {
char ac = i >= 0 ? a.charAt(i) : '0';
char bc = j >= 0 ? b.charAt(j) : '0';

int sum = (ac - '0') + (bc - '0') + carry;
result.append(sum % 2);
carry = sum / 2;
i--;
j--;
}

if (carry > 0) {
result.append(1);
}

return new String(result.reverse());
}
}