Add Binary (Java)

LeetCode

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

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

	/*
	Given two binary strings, return their sum (also a binary string).
	For example,
	a = "11"
	b = "1"
	Return "100".
	*/
	public class AddBinary {
	public String addBinary(String a, String b) {
	if (a==null ||a.length()==0){
	return b;
	}
	if (b==null || b.length()==0){
	return a;
	}
	StringBuilder sb=new StringBuilder();
	int lastA=a.length()-1;
	int lastB=b.length()-1;
	int carry=0;
	while (lastA>=0 ||lastB>=0 ||carry>0){
	int num1=lastA>=0?a.charAt(lastA--)-'0':0;
	int num2=lastB>=0?b.charAt(lastB--)-'0':0;
	int current=(num1+num2+carry)%2;
	carry=(num1+num2+carry)/2;
	sb.insert(0, current);
	}
	return sb.toString();
	}
	}

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