LeetCode-in-Java
191. Number of 1 Bits
Easy
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.
Follow up: If this function is called many times, how would you optimize it?
Solution
public class Solution {
public int hammingWeight(int n) {
int sum = 0;
boolean flag = false;
if (n < 0) {
flag = true;
n = n - Integer.MIN_VALUE;
}
while (n > 0) {
int k = n % 2;
sum += k;
n /= 2;
}
return flag ? sum + 1 : sum;
}
}