java 循环 习题

1、要求计算1！+2！+……10！的值

 

 

第一种是for循环：

public class TestXiti {
    public static void main(String[] args) {
        double sum=0.0;
        for(int i=0;i<=10;i++) {
             double temp=1.0;
        for(int j=1;j<=i;j++) {
             temp=temp*j;
        }
        sum+=temp;
        }
        System.out.println(sum);
    }
}

第二种是递归：

public class TestXiti {
    public static void main(String[] args) {
        System.out.println(mul(10));
    }
    public static double mul(int num) {
        if(num==1) {
            return fun(1);
        }
        return fun(num) +mul(num-1);
    }
    public static double fun(int num) {
        if(num==1) {
            return 1;
        }
        return num*fun(num-1);
    }
}

2、编写一个方法，此方法可以将一个整数二进制输出：

//for循环

public class TestXiti {
    public static void main(String[] args) {
            int t=11;
            String str="";
            while(t!=0) {
                str=(t%2)+str;
                t=t/2;
            }
            System.out.println(str);
    }
}
//递归

public class TestXiti {
    public static void main(String[] args) {
            toBanary(11);
    }
    public static void toBanary(int num ) {
        if(num/2==0) {
            System.out.print(num%2);
        }
        else {
            toBanary(num/2);
            System.out.print(num%2);
        }

    }
}

3、先给出2个数组，将2个数组合并后，升序输出：

　数组Ａ　{1,7,9,11,13,15,17,19};
  数组Ｂ  {2,4,6,8,10};

public class TestXiti {
    public static void main(String[] args) {
        int dataA[]=new int[] {1,7,9,11,13,15,17,19};
        int dataB[]=new int[] {2,4,6,8,10};
        int dataC[]=contact(dataA,dataB);
        java.util.Arrays.sort(dataC);
        print(dataC);
    }
    public static int[] contact(int arrA[],int arrB[]) {
        int arrC []=new int[arrA.length+arrB.length];
        System.arraycopy(arrA, 0, arrC, 0, arrA.length);
        System.arraycopy(arrB, 0, arrC, arrA.length, arrB.length);
        return arrC;
    }
    public static void print(int [] arr) {
        for(int x=0;x<arr.length;x++) {
                System.out.print(arr[x] + " ");
        }
    }
}

4、//数组转置

public class TestXiti {

    public static void main(String[] args) {

       int data[]=new int[] {1,2,3,4,5,6};

       reverse(data);

       print(data);

    }

    public static void reverse(int [] temp) {

       int center=temp.length / 2;

       int head=0;

       int tail=temp.length-1;

       for(int x=0;x

           int t=temp[head];

           temp[head]=temp[tail];

           temp[tail]=t;

           head++;

           tail--;

       }

    }

    public static void print(int [] arr) {

       for(int x=0;xlength;x++) {

           System.out.print(arr[x] + " ");

       }

    }

   

  }

 

5、去掉数组中的0；

public class TestXiti {

    public static void main(String[] args) {

       int oldArr[]=new int[] {1,3,4,5,0,0,6,6,0,5,4,7,6,7,0,5};

       int newArr[]=new int[count(oldArr)];

       copy(oldArr,newArr);

       print(newArr);

    }

    public static int count(int arr[]) {

       int sum=0;

       for(int i=0;ilength;i++) {

           if(arr[i]!=0)

              sum++;

       }

       return sum;

      

    }

    public static void copy(int oldArr [] , int newArr []) {

       int foot=0;

       for(int i=0;ilength;i++) {

           if(oldArr[i]!=0) {

              newArr[foot++]=oldArr[i];

           }

       }

    }

    public static void print(int [] arr) {

       for(int x=0;xlength;x++) {

           System.out.print(arr[x] + " ");

       }

    }

   

  }