給你兩個二進制字符串，返回它們的和（用二進制表示）。

輸入為 非空 字符串且只包含數字 1 和 0。

示例 1:

輸入: a = "11", b = "1"
輸出: "100"

示例 2:

輸入: a = "1010", b = "1011"
輸出: "10101"

提示：

• 每個字符串僅由字符 '0' 或 '1' 組成。
• 1 <= a.length, b.length <= 10^4
• 字符串如果不是 "0" ，就都不含前導零。

C#代碼

public class Solution {
public string AddBinary(string a, string b) {
int num1 = a.Length;
int num2 = b.Length;
int max = Math.Max(num1, num2);
int min = Math.Min(num1, num2);
string c = min == num1 ? a : b;
string d = min == num1 ? b : a;

    Stack<int> stack = new Stack<int>();
    bool isAdd = false;
    int val;

    for (int i = min - 1; i > -1; i--)
    {
        var val1 = c[i];
        var val2 = d[i + max - min];
        val = val1 ^ val2;
        stack.Push(isAdd ? (val ^ 1) : val);
        isAdd = val1 == '1' && val2 == '1' || val == 1 && isAdd;
    }

    for (int i = max - min - 1; i > -1; i--)
    {
        int.TryParse(d[i].ToString(), out val);
        stack.Push(isAdd ? (val ^ 1) : val);
        isAdd = d[i] == '1' && isAdd;
    }

    if (isAdd)
        stack.Push(1);

    StringBuilder sb = new StringBuilder();
    while (stack.Count > 0)
        sb.Append(stack.Pop());

    return sb.ToString();
}

}