Codewars Java练习：Bit Counting

题目

Write a function that takes an (unsigned) integer as input, and returns the number of bits that are equal to one in the binary representation of that number.

Example: The binary representation of 1234 is 10011010010, so the function should return 5 in this case

题解

我使用了每次右移，统计奇偶性的解法——

import java.util.*;
import java.io.*;

class BitCounting {

	public static int countBits(int n){
		int result = 0;
		while (n!=0) {
			if ((n&1) == 1) result ++;
			n >>= 1;
		}
		return result;
	}

}

标准解法中，我比较喜欢的有如下代码——

直接使用Integer的库函数

public class BitCounting {

  public static int countBits(int n){
    
    return Integer.bitCount(n);
  }
  
}

转换为字符串处理，其中用到了Java中的Lambda表达式

public class BitCounting {

  public static int countBits(int n){
    return (int) Integer.toBinaryString(n).chars()
              .filter(c -> c == '1')
              .count();
  }
  
}