[LeetCode]34. Add Binary二进制相加

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

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

解法：从后往前对两个string相加即可。注意将char转换为int，注意进位，注意结果顺序。

class Solution {
public:
    string addBinary(string a, string b) {
        int as = a.size(), bs = b.size();
        if (bs > as) return addBinary(b, a);
        int i = as - 1, j = bs - 1, carry = 0;
        string res = "";
        while (i >= 0)
        {
            int curr = (int)(a[i] - '0') + carry + (j >= 0 ? (int)(b[j] - '0') : 0);
            res += (char)(curr % 2 + '0');
            carry = curr / 2;
            i--; j--;
        }
        res = carry == 1 ? res + '1' : res;
        reverse(res.begin(), res.end());
        return res;
    }
};

或者直接使用string的insert成员函数：

class Solution {
public:
    string addBinary(string a, string b) {
        int as = a.size(), bs = b.size();
        if (bs > as) return addBinary(b, a);
        int i = as - 1, j = bs - 1, carry = 0;
        string res = "";
        while (i >= 0)
        {
            int curr = (int)(a[i] - '0') + carry + (j >= 0 ? (int)(b[j] - '0') : 0);
            res.insert(0, 1, (char)(curr % 2 + '0'));
            carry = curr / 2;
            i--; j--;
        }
        res = carry == 1 ? res.insert(0, 1, '1') : res;
        return res;
    }
};