java中实现递归计算二进制表示中1的个数

借助Java语言，运用递归算法计算整数N的二进制表示中1的个数

/*use the recursive algorithme to calculate
* the number of "1" in the binary expression
* of an Integer N.
* Note:if N is an odd, then
* the result is the result of N/2 plus 1.
* And the program use the bit operation to
* improve efficency ,though it's seemingly
* not necessary ,but the idea I think is good.
* The program is writed by Zewang Zhang ,at
* 2015-5-4,in SYSU dorms.
*/
public class CalculateNumberInBinaryExpression {
//Main method.
public static void main(String[] args) {
//For example ,make N equals 13 ,the result shows 3
System.out.println(numOfEven(13));
//For example ,make N equals 128 ,the result shows 1
System.out.println(numOfEven(128));
}
//The static method of numOfEven is the recursive method.
public static int numOfEven(int x) {
//The base of recursive.
if(x==0) {
return 0;
}
//If x is an odd.
else if(x%2!=0) {
return numOfEven(x>>1)+1;
}
//If x is an even except 0.
else {
while(x%2==0) {
x=(x>>1);
}
return numOfEven(x);
}
}
}

来个最简单的，不过未测试：）

public int a(int i){
if(i==0||i==1) return i;
return i%2+a(i/2);
}

以上所述就是本文的全部内容了，希望大家能够喜欢。

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