CODE 67: Add Binary

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

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

public String addBinary(String a, String b) {// Note: The Solution object is instantiated only once and is reused by// each test case.char[] as = a.toCharArray();char[] bs = b.toCharArray();int i = as.length - 1;int j = bs.length - 1;int c = 0;StringBuilder sb = new StringBuilder();while (i >= 0 && j >= 0) {if (0 == c) {if ((as[i] == '0' && bs[j] == '1')|| (as[i] == '1' && bs[j] == '0')) {sb = sb.insert(0, '1');c = 0;} else if ((as[i] == '0' && bs[j] == '0')) {sb = sb.insert(0, '0');c = 0;} else {sb = sb.insert(0, '0');c = 1;}} else if (1 == c) {if ((as[i] == '0' && bs[j] == '1')|| (as[i] == '1' && bs[j] == '0')) {sb = sb.insert(0, '0');c = 1;} else if ((as[i] == '0' && bs[j] == '0')) {sb = sb.insert(0, '1');c = 0;} else {sb = sb.insert(0, '1');c = 1;}}i--;j--;}while (i >= 0) {if (0 == c) {sb = sb.insert(0, as[i]);c = 0;} else if (1 == c) {if (as[i] == '0') {sb = sb.insert(0, '1');c = 0;} else {sb = sb.insert(0, '0');c = 1;}}i--;}while (j >= 0) {if (0 == c) {sb = sb.insert(0, bs[j]);c = 0;} else if (1 == c) {if (bs[j] == '0') {sb = sb.insert(0, '1');c = 0;} else {sb = sb.insert(0, '0');c = 1;}}j--;}if (1 == c) {sb = sb.insert(0, '1');}return sb.toString();}