371. Sum of Two Integers

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.

Solution:

当a和b相加的每一位都没有carry的时候（ab：01/10/00），a+b的和就等于 a^b，

把b当成一个carry开始，求它与a的和，就是要求不算carry的值（a^b），再加上更新后的carry（a&b << 1)

public int getSum(int a, int b) {
        while(b!=0){
            int carry = (a&b)<<1;
            a = a^b;
            b = carry;
        }  
        return a;
    }