LeetCode(56)-Add Binary

题目：

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

For example,
a = "11"
b = "1"
Return "100".

思路：

代码：

public class Solution {
public String addBinary(String a, String b) {
if(a.length() < b.length()){
String tmp = a;
a = b;
b = tmp;
}
int lengthA = a.length()-1;
int lengthB = b.length()-1;
int carry = 0;
String all = "";
while(lengthB >= 0){
int num = (int)(a.charAt(lengthA)-'0')+(int)(b.charAt(lengthB)-'0')+carry;
int k = num%2;
carry = num/2;
all = String.valueOf(k)+all;
lengthA--;
lengthB--;
}
while(lengthA >= 0){
int num = (int)(a.charAt(lengthA)-'0')+carry;
int k = num%2;
carry = num/2;
all = String.valueOf(k)+all;
lengthA--;
}
if(carry == 1){
all = "1"+all;
}
return all;
}
}