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package com.congli.leetcode;

/**

* Practiced on 11/19/2012.

*

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

* For example,

* a = "11"

* b = "1"

* Return "100"

*/

public class AddBinary {

public static void main(String[] args)

{

AddBinary sl = new AddBinary();

System.out.println(sl.addBinary("1", "111"));

}

public String addBinary(String a, String b) {

if(a == null || a == "") return b;

if(b == null || a == "") return a;

char[] resultChar = new char[Math.max(a.length(), b.length())+1];

resultChar[0] = '0';

int aInd = a.length()-1;

int bInd = b.length()-1;

char[] carry = {'0'};

for(int i = Math.max(aInd, bInd)+1; i >= 0; --i)

{

if(aInd < 0 && bInd < 0) resultChar[i] = carry[0];

else if(aInd < 0) resultChar[i] = helper(b.charAt(bInd--), '0', carry);

else if(bInd < 0) resultChar[i] = helper(a.charAt(aInd--), '0', carry);

else resultChar[i] = helper(a.charAt(aInd--), b.charAt(bInd--), carry);

}

String result = "";

for(int i = (resultChar[0] == '0' ? 1 : 0); i < resultChar.length; ++i)

{

result += resultChar[i];

}

return result;

}

private char helper(char a, char b, char[] carry)

{

if(a == b)

{

char result = carry[0] == '1' ? '1' : '0';

carry[0] = a == '1' ? '1' : '0';

return result;

}

else return carry[0] == '1' ? '0' : '1';

}

}