lintcode-easy-Add Binary

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

 Example

a = 11

b = 1

Return 100

 

这道题也没太多好说的……

public class Solution {
    /**
     * @param a a number
     * @param b a number
     * @return the result
     */
    public String addBinary(String a, String b) {
        // Write your code here
        
        if(a == null)
            return b;
        if(b == null)
            return a;
        
        if(a.length() == 0)
            return b;
        if(b.length() == 0)
            return a;
        
        int p1 = a.length() - 1;
        int p2 = b.length() - 1;
        
        StringBuilder result = new StringBuilder();
        
        int carry = 0;
        
        while(p1 >= 0 || p2 >= 0){
            int bit_a = 0;
            int bit_b = 0;
            
            if(p1 >= 0){
                bit_a = (int) (a.charAt(p1) - '0');
                p1--;
            }
            if(p2 >= 0){
                bit_b = (int) (b.charAt(p2) - '0');
                p2--;
            }
            
            result.insert(0, (bit_a + bit_b + carry) % 2);
            carry = (bit_a + bit_b + carry) / 2;
            
        }
        
        if(carry == 1)
            result.insert(0, 1);
        
        return result.toString();
    }
}