/**  * 快速計算二進制數中1的個數(Fast Bit Counting)  * 該算法的思想如下：  * 每次將該數與該數減一后的數值相與，從而將最右邊的一位1消掉  * 直到該數為0  * 中間循環的次數即為其中1的個數  * 例如給定"10100“，減一后為”10011",相與為"10000",這樣就消掉最右邊的1  * Sparse Ones and Dense Ones were first described by Peter Wegner in  * “A Technique for Counting Ones in a Binary Computer“,  * Communications of the ACM, Volume 3 (1960) Number 5, page 322  */ package al; public class CountOnes {  public static void main(String[] args) {   int i = 7;   CountOnes count = new CountOnes();   System.out.println("There are " + count.getCount(i) + " ones in i");  }  /**   * @author   * @param i 待測數字   * @return 二進制表示中1的個數   */  public int getCount(int i) {     int n;   for(n=0; i > 0; n++) {    i &= (i - 1);   }     return n;    } }