问题描述:
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
解题思路:
我们知道，机器内部是使用二进制表示数字，其中整数用补码表示。既然不能直接调用系统实现好的十进制“+、-”运算符，那就可以考虑自己实现补码加法，对于使用补码表示的整数有以下性质：[X]补 + [Y]补 = [X+Y]补
示例代码:
class Solution {
public:
int getSum(int a, int b) {
int result = 0;
int flag = 0, jie = 1;
for (int i = 0; i < 32; i++){
int lastA = a & 1;
int lastB = b & 1;
if (flag == 1) {
if (lastA == 1 && lastB == 1) {
flag = 1;
result |= jie;
}
else if (lastA == 0 && lastB == 0) {
flag = 0;
result |= jie;
}
else {
flag = 1;
}
}
else {
if (lastA == 1 && lastB == 1) {
flag = 1;
}
else if (lastA == 0 && lastB == 0) {
flag = 0;
}
else {
flag = 0;
result |= jie;
}
}
jie *= 2;
a = a >> 1;
b = b >> 1;
}
if (flag) {
result |= jie;
}
return result;
}
};