67. Add Binary

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

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

和415的解法一样

class Solution {

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

????????StringBuilder sb = new StringBuilder();

????????int i = a.length() - 1;

????????int j = b.length() - 1;

????????int carry = 0;

????????for(; i >= 0 || j >= 0 || carry == 1; i--,j--){

????????????int x = i < 0 ? 0 : a.charAt(i) - ‘0‘;

????????????int y = j < 0 ? 0 : b.charAt(j) - ‘0‘;

????????????sb.append((x + y + carry) % 2); //除去进位后的值?

????????????carry = (x + y + carry) / 2; //算出进位值

????????}

????????return sb.reverse().toString();

????}

}