BitAdd.ava 328mm

public class Solution {
    public String addBinary(String a, String b) {
        int i = a.length()-1;
		int j = b.length()-1;
		int n = j>i?j:i;
		int sum = 0;
		int adv = 0;
		int aa;
		int ab;
		int al = i;
		int bl =j;
		StringBuffer result = new StringBuffer();
		for(int ik = n ;ik>=0 ;ik--){
	aa =	al<0 ?  0 : 
									a.charAt(al--)=='0'? 0:1;
				ab = 	bl<0?  0 : 
									b.charAt(bl--)=='0'? 0:1;
		sum = aa + ab + adv;
		result.append(sum%2==1? '1':'0');
		adv = sum >> 1 ;
		}
		if (adv == 1) result.append('1');
		return result.reverse().toString();
    }
}