LintCode刷題之路（一）：A+B問題

C++：

class Solution {
public:
    /**
     * @param a: An integer
     * @param b: An integer
     * @return: The sum of a and b 
     */
    int aplusb(int a, int b) {
        // write your code here
        int sum_1 = 0;
        int carry = 0;
        if(a==0){
            return b;
        }
        else if(b==0){
            return a;
        }
        else
        {
            sum_1 = a^b; //異或操作，沒有進位的和
            carry = (a&b)<<1; //進位位
            return aplusb(sum_1,carry); //知道進位位爲0，遞歸結束
        }
    }
};

Py3:

class Solution:
    """
    @param a: An integer
    @param b: An integer
    @return: The sum of a and b 
    """
    def aplusb(self, a, b):
        # write your code here
        if a==0:
            return b
        elif b==0:
            return a
        sum_ = a^b
        carry_ = (a&b)<<1
        return Solution().aplusb(sum_,carry_)