共计 741 个字符，预计需要花费 2 分钟才能阅读完成。
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”
难度: easy
题目：给定两个二进制字符串，返回它们的和（也是二进制字符串）。字符串都不为空且只有 0､1 组成。
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());
}
}
