[Leetcode] Number of 1 Bits 关于位操作的思考

Number of 1 Bits

Write a function that takes an unsigned integer and returns the number of ’1‘ bits it has (also known as the Hamming weight).

For example, the 32-bit integer ’11‘ has binary representation 00000000000000000000000000001011, so the function should return 3.

这个题目的解法还是很清楚的

一、整数不变，mask右移

使用一个mast不断与这个数字进行与操作，得到相应的bit是否是零

int mask = 1;

int num;

int count = 0;

for shift=0:31

mask = mask << shift

int bit = num & mask;

if bit!=0

count++;

end

end

二、mask不变，整数右移法。

这里只适合整数非负的情况，负数右移，符号位会被不断复制，最后变为全一。