位运算

基础知识

Test kth bit is set: num & (1 << k) != 0.

Set kth bit: num |= (1 << k).

Turn off kth bit: num &= ~(1 << k).

Toggle the kth bit: num ^= (1 << k).

To check if a number is a power of 2, num & num - 1 == 0.

x  & x-1 can set the rightest 1 to 0

x ^ x = 0

x ^ 0 = x

如何用位运算实现加减乘除？

如何用位运算

LC 136 Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

正常想这道题几乎无解，不用多余内存基本上限定了原地hash，但是这道题又没有给出数字的具体范围。

这道题很tricky，利用了x^x = 0的特性，把所有的值挨个做异或，即可得到那个落单的值。