问题描述：

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

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

思路： 采用二进制加法的思路;

代码：

public class AddBinary {  //java
	 public String addBinary(String a, String b) {
		 if(a == null || a.trim().isEmpty())
			 return b.trim();
		 if(b == null || b.trim().isEmpty())
			 return a.trim();
		 
		 String result = "";
		 
		 int carry = 0;
		 int alen = a.length();
		 int blen = b.length();
		 
		 int maxLen = Math.max(alen, blen);
		 for(int i = 0; i< maxLen; i++){
			 int tmpa = ((i<alen)?a.charAt(alen-1-i)-'0':0);
			 int tmpb = ((i<blen)?b.charAt(blen-1-i)-'0':0);
			 int sum = tmpa+tmpb+carry;
			 
			 if(sum >=2){
				 result = (sum%2) + result;
				 carry = 1;
			 }
			 else {
				 result = sum + result;
				 carry = 0;
			 }
		 }
		 
		
		 if(carry == 1)
			 result = "1"+result;
		 return result;
	 }
	 
	 public static void main(String [] args){
		 AddBinary ab = new AddBinary();
		 System.out.println(ab.addBinary("11", "1"));
	 }
}

[leetcode]Add Binary