191. Number of 1 Bits
Write a function that takes an unsigned integer and return the number of ‘1‘ bits it has (also known as the Hamming weight).
Example 1:
Input: 00000000000000000000000000001011
Output: 3
Explanation: The input binary string 00000000000000000000000000001011 has a total of three ‘1‘ bits.
Example 2:
Input: 00000000000000000000000010000000 Output: 1 Explanation: The input binary string 00000000000000000000000010000000 has a total of one ‘1‘ bit.
Example 3:
Input: 11111111111111111111111111111101 Output: 31 Explanation: The input binary string 11111111111111111111111111111101 has a total of thirty one ‘1‘ bits.
Note:
-3.
Follow up:
If this function is called many times, how would you optimize it?
package leetcode.easy;
public class NumberOf1Bits {
// you need to treat n as an unsigned value
public int hammingWeight1(int n) {
int bits = 0;
int mask = 1;
for (int i = 0; i < 32; i++) {
if ((n & mask) != 0) {
bits++;
}
mask <<= 1;
}
return bits;
}
public int hammingWeight2(int n) {
int sum = 0;
while (n != 0) {
sum++;
n &= (n - 1);
}
return sum;
}
@org.junit.Test
public void test() {
System.out.println(hammingWeight1(-3));
System.out.println(hammingWeight2(-3));
}
}
LeetCode_191. Number of 1 Bits
原文：https://www.cnblogs.com/denggelin/p/11706513.html