java中实现递归计算二进制表示中1的个数

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 Ihttp:// 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 http://int a(int i){

if(i==0||i==1) return i;

return i%2+a(i/2);

}

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