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/**

* Created by codingBoy on 17/2/7.

*/

public class addBinary

{

/**

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

For example,

a = "11"

b = "1"

Return "100".

* @param args

*

* 即二进制的加法

*/

public static void main(String[] args)

{

System.out.println(addBinary("11011","101"));

}

/**

* carry用于纪录超过该位数字超过2的，向前进1

*

* @param a

* @param b

* @return

*/

public static String addBinary(String a, String b) {

StringBuilder sb = new StringBuilder();

int i = a.length() - 1, j = b.length() -1, carry = 0;

while (i >= 0 || j >= 0) {

int sum = carry;//将进的1赋给sum

//这里需要注意的是，字符'1'的ASCAI＝49，'0'＝48，当然我不清楚这里后面为啥要减去一个'0'，因为直接输入'1'的话输出的是0而不是49.

if (j >= 0) sum += b.charAt(j--) - '0';

if (i >= 0) sum += a.charAt(i--) - '0';

sb.append(sum % 2);//将两个二进制从右向左进行求和，并将每次结果纪录在sb中，所以最后肯定要将sb逆转。

carry = sum / 2;

}

if (carry != 0) sb.append(carry);

return sb.reverse().toString();

}

}