【LeetCode】Add Binary

Add Binary 
Total Accepted: 11726 Total Submissions: 45895 My Submissions
Given two binary strings, return their sum (also a binary string).
For example,
a = "11"
b = "1"
Return "100".
【解题思路】
二进制加法，转为数组，按位相加，return字符串即可。

Java AC 444ms

public class Solution {
    public String addBinary(String a, String b) {
		if (a == null || b == null) {
			return "";
		}
		if ("".equals(a) || "".equals(b)) {
			return "";
		}
		if ("".equals(a.replaceAll("0", ""))
				&& "".equals(b.replaceAll("0", ""))) {
			return "0";
		}
		int len1 = a.length();
		int len2 = b.length();
		char arrayA[] = a.toCharArray();
		char arrayB[] = b.toCharArray();
		int maxLen = Math.max(len1, len2);
		int array[] = new int[maxLen + 1];
		int k = maxLen;
		while (len1 > 0 && len2 > 0) {
			array[k] += arrayA[len1-1] - '0' + arrayB[len2-1] - '0';
			if (array[k] >= 2) {
				array[k] -= 2;
				array[k - 1] += 1;
			}
			k--;
			len1--;
			len2--;
		}
		while (len1 > 0) {
			array[k] += arrayA[len1-1] - '0';
			if (array[k] >= 2) {
				array[k] -= 2;
				array[k - 1] += 1;
			}
			len1--;
			k--;
		}
		while (len2 > 0) {
			array[k] += arrayB[len2-1] - '0';
			if (array[k] >= 2) {
				array[k] -= 2;
				array[k - 1] += 1;
			}
			len2--;
			k--;
		}
		StringBuffer sb = new StringBuffer();
		int i = 0;
		if (array[0] == 0) {
			i = 1;
		}
		for (; i < maxLen + 1; i++) {
			sb.append(array[i]);
		}
		return sb.toString();
	}
}

Python AC 228ms

class Solution:
    # @param a, a string
    # @param b, a string
    # @return a string
    def addBinary(self, a, b):
        len1 = len(a)
        len2 = len(b)
        if len1 > len2:
            maxLen = len1
        else:
            maxLen = len2
        list = [0 for i in range(maxLen + 1)]
        k = maxLen
        while len1 > 0 and len2 > 0:
            list[k] += int(a[len1-1]) + int(b[len2-1])
            if list[k] >= 2:
                list[k] -= 2
                list[k-1] += 1
            len1 -= 1
            len2 -= 1
            k -= 1
        while len1 > 0:
            list[k] += int(a[len1-1])
            if list[k] >= 2:
                list[k] -= 2
                list[k-1] += 1
            len1 -=1
            k -= 1
        while len2 > 0:
            list[k] += int(b[len2-1])
            if list[k] >= 2:
                list[k] -= 2
                list[k-1] += 1
            len2 -= 1
            k -= 1
        list = [str(e) for e in list]
        if list[0] == '0':
            return "".join(list[1:])
        else:
            return "".join(list)