leetcode:67. Add Binary

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

For example,
a = "11"
b = "1"

Return "100".

題意&解題思路：

字符串形式的二進制相加，暴力解決。注意處理多餘的前導零。代碼如下：

class Solution {
public:
    string addBinary(string a, string b) {
        int la = a.length() - 1;
        int lb = b.length() - 1;
        string c = "";
        int cc = 0, dd = 0;
        while(la >= 0 && lb >= 0){
            dd = (a[la--] - '0' + b[lb--] - '0' + cc);
            cc = dd/2;
            dd %= 2;
            c += to_string(dd);
        }
        while(la >= 0){
            dd = (a[la--] - '0' + cc);
            cc = dd/2;
            dd %= 2;
            c += to_string(dd);
        }
        while(lb >= 0){
            dd = (b[lb--] - '0' + cc);
            cc = dd/2;
            dd %= 2;
            c += to_string(dd);
        }
        if(cc)c += "1";
        int i = 0, j = c.length() - 1;
        while(c[j] == '0')j--;
        c = c.substr(0, j + 1);
        if(!c.length())return "0";
        while(i < j){
            c[j] = c[i] + c[j] - (c[i] = c[j]);
            i++, j--;
        }
        return c;
    }
};