Leetcode之Add Binary

題目：

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"

代碼：

class Solution {
public:
    string addBinary(string a, string b) {
        string res;
	int alen = a.size();
	int blen = b.size();
	int temp = 0;
	for (int i = alen - 1, j = blen - 1; i >= 0 || j >= 0; i--, j--) {
		int ai = 0, bi = 0, t = 0;
		if (i >= 0 && j >= 0) {
			ai = a[i] -'0';
			bi = b[j] - '0';
			t = ai + bi + temp;
		}
		else if (i >= 0) {
			ai = a[i] - '0';
			t = ai + temp;
		}
		else {
			bi = b[j] - '0';
			t = bi + temp;
		}
		res += to_string(t % 2);
		temp = t / 2;
	}
	if (temp > 0) {
		res += to_string(temp);
	}

	int len = res.size();
	for (int i = 0; i < len / 2; i++) {
		int j = len - 1 - i;
		char temp = res[i];
		res[i] = res[j];
		res[j] = temp;
	}

	return res;
    }
};