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).
Note:
Note that in some languages, such as Java, there is no unsigned integer type. In this case, the input will be given as a signed integer type. It should not affect your implementation, as the integer's internal binary representation is the same, whether it is signed or unsigned.
In Java, the compiler represents the signed integers using 2's complement notation. Therefore, in Example 3, the input represents the signed integer. -3.
Example 1:
Input: n = 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three '1' bits.
Example 2:
Input: n = 00000000000000000000000010000000
Output: 1
Explanation: The input binary string 00000000000000000000000010000000 has a total of one '1' bit.
Example 3:
Input: n = 11111111111111111111111111111101
Output: 31
Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one '1' bits.
Constraints:
The input must be a binary string of length 32.
思路一：用 n & 1 == 1 判断 1 的 bit 位，然后用 >>> 遍历 n 的所有位数
public int hammingWeight(int n) {
int weight = 0;
while (n != 0) {
if ((n & 1) == 1) weight++;
n >>>= 1;
}
return weight;
}
思路二：看了题解，发现还有一种位运算操作， n & n - 1 每一次操作都会消除 n 的最后一位 bit 位，循环操作即可
public int hammingWeight(int n) {
int res = 0;
while (n != 0) {
res += 1;
n &= n - 1;
}
return res;
}