Number of 1 Bits
描述
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.
分析
最直接的方法,做32次右移,统计出1的个数。
第二个方法,来自 "Hacker's Delight" 这本书。
使用Java解题时,需要注意:
- 输入值n可能为负数,但应视其为无符号整数,因为Java中实际上是没有无符号整数的
- 使用无符号右移操作符
>>>
,可以忽略符号位
解法1
// Number of 1 Bits
// Time Complexity: O(32), Space Complexity: O(1)
public class Solution {
// you need to treat n as an unsigned value
public int hammingWeight(int n) {
int count = 0;
for (int i = 0; i < 32; ++i) {
count += n & 1;
n >>>= 1;
}
return count;
}
}
解法2
// Number of 1 Bits
// Time Complexity: O(number of 1), Space Complexity: O(1)
public class Solution {
// you need to treat n as an unsigned value
public int hammingWeight(int n) {
int count = 0;
while (n != 0) {
++count;
n &= n - 1;
}
return count;
}
}