[LeetCode] Sum of Two Integers 两数之和

Calculate the sum of two integers a and b, but you are not allowed to use the operator + and -.

Example:
Given a = 1 and b = 2, return 3.

Credits:
Special thanks to @fujiaozhu for adding this problem and creating all test cases.

这道题是CareerCup上的一道原题，难道现在LeetCode的新题都是到处抄来的么，讲解可以参见我之前的博客18.1 Add Two Numbers。简而言之就是用异或算不带进位的和，用与并左移1位来算进位，然后把两者加起来即可，先来看递归的写法如下：

解法一：

class Solution {
public:
    int getSum(int a, int b) {
        if (b == 0) return a;
        int sum = a ^ b;
        int carry = (a & b) << 1;
        return getSum(sum, carry);
    }
};

上面的解法可以精简到一行，哈哈，叼不叼？

解法二：

class Solution {
public:
    int getSum(int a, int b) {
        return b == 0 ? a : getSum(a ^ b, (a & b) << 1);
    }
};

也可以写成迭代的样子，思路都是一样的~

解法三：

class Solution {
public:
    int getSum(int a, int b) {
        while (b) {
            int carry = (a & b) << 1;
            a = a ^ b;
            b = carry;
        }
        return a;
    }
};

参考资料：

http://www.cnblogs.com/grandyang/p/5451942.html

https://leetcode.com/discuss/111682/one-line-java-code

https://leetcode.com/discuss/111601/6-line-java-solution

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