[Leetcode] Add Binary

Add Binary

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

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

思路： 对齐， 计算当前位和进位；

             如果位较长，让我想到了先行进位加法器，不过这里的计算不能并行，也无什么效果。

//add Binary
class Solution {
public:
    string addBinary(string a, string b) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
			string c;
			int flag=0;
			int lena = a.size();
			int lenb = b.size();
			int len = abs(lena-lenb);
			string append(len,'0');
			if(lena>lenb){
				b = append + b;
				c.resize(lena,'0');
			}else{
				a = append + a;
				c.resize(lenb,'0');
			}
			for(int j=c.size()-1;j>=0;j--){
				int current = (a[j]-'0') ^(b[j]-'0') ^flag;
				if((a[j]-'0') +(b[j]-'0') +flag >1)
					flag = 1;
				else 
					flag = 0;
				c[j] = current+'0';
			}
			if(flag == 1)
				c = '1'+ c;
			
			return c;
			
    }
};