Add Binary

题目

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

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

分析

1. convert String to char array for a, b
2. initializ m , n to be the length of a, b
3. new a StringBuilder, in order to append and insert String easily
4. while loop to traverse every digit of a, b from rightmost to leftmost, including considering about a carry
5. pay attention to converting binary to decimal, using Character.forDigit

图解

解法

class Solution {   
    public String addBinary(String a, String b) {
        char[]arrayA = a.toCharArray();
        char[] arrayB = b.toCharArray();

        int m = a.length()-1;
        int n = b.length()-1;
        int carry= 0;

        StringBuilder sb = new StringBuilder();

        while(m>=0 || n>=0 || carry>0){
            int updateA = m>=0 ? arrayA[m--]-'0' : 0;
            int updateB = n>=0 ? arrayB[n--]-'0' : 0;

            int sum = updateA + updateB + carry;
            sb.insert(0,Character.forDigit(sum%2, 10)); // 用Character.forDigit 因为此题涉及到二进制转十进制
            carry = sum /2;
        }
        return  sb.toString();      
    }
}