LeetCode 191. Number of 1 Bits（比特数）

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原题网址：https://leetcode.com/problems/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.

方法一：直接点数。

public class Solution {    // you need to treat n as an unsigned value    public int hammingWeight(int n) {        int counts = 0;        int h = 1 << 31;        for(int i=0; i<32; i++) {            if ((n & h) != 0) counts ++;            n <<= 1;        }        return counts;    }}

方法二：采用n & -n的方法求得最低位的1。

public class Solution {    // you need to treat n as an unsigned value    public int hammingWeight(int n) {        int counts = 0;        boolean neg = n >= 0 ? false : true;        n &= Integer.MAX_VALUE;        long m = n;        if (neg) m |= (long)1 << 31;        while (m != 0) {            long lo = m & -m;            if (lo != 0) counts ++;            m ^= lo;        }        return counts;    }}

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