JAVA语言程序设计课后习题----第五单元解析（仅供参考）

1　　　　本题是水题，题目要求你求最大值、最小值，建议你用Arrays.sort函数进行排序，最大值、最小值就可以确定了

import java.util.Arrays;
import java.util.Scanner;

public class paone {
    public static void main(String[] args) {
       int [] aa = new int[5];
       double sum = 0.0;
       Scanner input =new Scanner(System.in);
        for (int i = 0; i <5 ; i++) {
            aa[i] = input.nextInt();
            sum += aa[i];
        }
        Arrays.sort(aa);
        for (int a : aa)
            System.out.print(a+" ");
        System.out.println();
        System.out.println("最小值:"+aa[0]);
        System.out.println("最大值:"+aa[4]);
        System.out.println("平均值:"+sum/5);
    }
}

2　　本题建议用swtich函数进行统计1-6的整数，每次产生一个随机数，就进行+1，switch中进行统计数目的大小建议用素组来定义。

import java.util.Random;

public class potwo {
    public static void main(String[] args) {
        Random r = new Random();
        int [] a =new int[1000];
        int [] b =new int[6];
        int count = 0;
        for (int i = 0; i < 1000; i++) {
            a[i] = r.nextInt(6)+1;
            switch (a[i]){
                case 1:
                    b[0]++;
                    break;
                case 2:
                    b[1]++;
                    break;
                case 3:
                    b[2]++;
                    break;
                case 4:
                    b[3]++;
                    break;
                case 5:
                    b[4]++;
                    break;
                case 6:
                    b[5]++;
                    break;
            }
        }
        for (int A : a){
            count++;
            System.out.print(A+" ");
            if (count % 10 == 0)
                System.out.println();
        }
        System.out.println("1的个数为"+b[0]);
        System.out.println("2的个数为"+b[1]);
        System.out.println("3的个数为"+b[2]);
        System.out.println("4的个数为"+b[3]);
        System.out.println("5的个数为"+b[4]);
        System.out.println("6的个数为"+b[5]);
    }
}

3　　本题水题，还是用sort函数进行排序，直接找到最小元素

import java.util.Arrays;
import java.util.Scanner;

public class pothree {
    public static void main(String[] args) {
        double [] arrays = new double[5];
        Scanner input = new Scanner(System.in);
        for (int i = 0; i <5 ; i++) {
            arrays[i]=input.nextDouble();
        }
        System.out.println("这个元素最小值是:"+min(arrays));
    }
    public static double min(double[] array){
        Arrays.sort(array);
        return array[0];
    }
}

4　　本题水题根据题目意思写即可，注意交换位置如何交换 a ^= b;　b ^= a;　a ^= b;

import java.util.Scanner;

public class pofour {
    public static void main(String[] args) {
        int [] aa = new int[10];
        Scanner input =new Scanner(System.in);
        for (int i = 0; i < 10 ; i++) {
            aa[i] = input.nextInt();
        }
        System.out.println("排序前的元素:");
        for (int A : aa)
            System.out.print(A+" ");
        System.out.println();
        for (int i = 0; i < 4 ; i++) {
            aa[i] ^= aa[9-i];
            aa[9-i] ^= aa[i];
            aa[i] ^= aa[9-i];
        }
        System.out.println("交换后的元素:");
        for (int A : aa)
            System.out.print(A+" ");
    }
}

5　　理解题目意思即可

import java.util.Scanner;

public class pofive {
    public static void main(String[] args) {
        int [] aa = new int[8];
        Scanner input =new Scanner(System.in);
        for (int i = 0; i < 8; i++) {
            aa[i]=input.nextInt();
        }
        System.out.println("选择排序前:");
        for (int A : aa)
            System.out.print(A+" ");
        System.out.println();
        for (int i = 0; i < 7; i++) {
            int k = i;
            for (int j = k+1; j < 8 ; j++) {
                if (aa[j] < aa[k])
                    k = j;
            }

            if (i!=k) {
                aa[i] ^= aa[k];
                aa[k] ^= aa[i];
                aa[i] ^= aa[k];
            }
           /* for (int A : aa)
                System.out.print(A+" ");
            System.out.println();*/
        }
        System.out.println("选择排序后:");
        for (int A : aa)
            System.out.print(A+" ");
    }
}

6　　根据题目意思，把Fibonacci数列意思理解即可

public class posix {
   public int [] aa = new int[20];
    public static void main(String[] args) {
        posix posix =new posix();
        int i,count=0;
        for (i = 0; i < 20; i++) {
            System.out.print(posix.fic(i)+" ");
            count++;
            if (count % 10 ==0)
                System.out.println();
        }


    }
    public int fic(int n){
        if (n==0)
            return aa[n]=1;
        if (n==1)
            return aa[n]=1;
        else
            return fic(n-2)+fic(n-1);
    }
}

7　　本题有点坑，你写的可能只是一种结果，因为你定义a、b两个数组，两个数组的长度有三种可能 a>b;a=b;a<b;三种可能，注意即可

import java.util.Scanner;

public class Poseven {
    public static void main(String[] args) {
        //int [] aa ={1,2,3,4,15};
        //int [] bb ={4,5,6,7};

        int a,b;
        Scanner input = new Scanner(System.in);



        System.out.print("请输入第一个数组的元素个数：");
        a=input.nextInt();
        System.out.print("请输入第二个数组的元素个数：");
        b=input.nextInt();
        int []aa=new int[a];
        int []bb=new int[b];
        System.out.println("请输入第一个数组的元素：");
        for (int i = 0; i < a; i++) {
          aa[i] = input.nextInt();
        }
        System.out.println("请输入第二个数组的元素：");
        for (int i = 0; i < b; i++) {
            bb[i] = input.nextInt();
        }
        System.out.println("加之前两个数组分别为:");
        for (int AA : aa)
            System.out.print(AA+" ");
        System.out.println();
        for (int BB : bb)
            System.out.print(BB+" ");
        System.out.println();
        System.out.println("相加后数组为:");
        Poseven poseven =new Poseven();
       int []abs= poseven.sumAraay(aa,bb);
       for (int ABS : abs)
           System.out.print(ABS+" ");


    }
    public static int[] sumAraay(int [] a,int [] b){
        int max,min;
        max = a.length >= b.length ? a.length:b.length;
        min = a.length <  b.length ? a.length:b.length;
        int leng1=a.length,leng2=b.length;
        int sum []=new int[max];
        for (int i = 0; i < min; i++) {
            sum[i] = a[i]+b[i];
            leng1--;
            leng2--;
        }
        for (int j = min; j < max; j++) {
            if (leng1==0)
                sum[j] = b[j];
            else
                sum[j] = a[j];
        }
       /* for (int SUM : sum)
            System.out.print(SUM+" ");
        System.out.println();*/
        return sum;

    }

}

8　　定义一个可以放下这两个素组大小的素组，记录一个数组存完后，这个素组的下标即可

import java.util.Arrays;

public class Poeight {
    public static void main(String[] args) {
        Poeight poeight =new Poeight();
        int [] aa = {1,10,3,4};
        int [] bb = {4,5,6,7,8};
        System.out.println("和成前的数组分别为:");
        for (int AA : aa)
            System.out.print(AA+" ");
        System.out.println();
        for (int BB : bb)
            System.out.print(BB+" ");
        System.out.println();
        System.out.println("合成后的数组为:");
        int [] merge=poeight.arrayMerge(aa,bb);
        for (int MERGE : merge)
            System.out.print(MERGE+" ");
        System.out.println();

    }
    public static int [] arrayMerge(int [] a,int [] b){
        int sum=a.length+b.length;
        int [] suml = new int[sum];
        int min = a.length < b.length ? a.length:b.length;
        int max = a.length >= b.length ? a.length:b.length;
        for (int i = 0; i < min ; i++) {
            if (a.length < b.length)
            suml[i] = a[i];
            else
                suml[i] = b[i];
        }
        for (int i = min; i < sum; i++) {
            if (a.length>b.length)
            suml[i] = a[i-b.length];
            else
                suml[i] = b[i-a.length];
        }
        Arrays.sort(suml);
        return suml;
    }
}

9　　根据题目意思，直接求解即可

import java.util.Scanner;

public class Ponine {
    public static void main(String[] args) {
        double [] aa = new double[3];
        double [] bb = new double[3];
        Scanner input = new Scanner(System.in);
        System.out.print("请依次输入a,b,c的值:");
        aa[0] = input.nextDouble();
        aa[1] = input.nextDouble();
        aa[2] = input.nextDouble();
        double x1 =( -aa[1]+Math.sqrt(Math.pow(aa[1],2)-4*aa[0]*aa[2]))/2*aa[0];
        double x2 =( -aa[1]-Math.sqrt(Math.pow(aa[1],2)-4*aa[0]*aa[2]))/2*aa[0];
        bb[0]=x1;
        bb[1]=x2;

        System.out.println("根的个数为"+ solveQuadratic(aa,bb));

    }
    public static int solveQuadratic(double [] eqn, double [] roots){
        int solve=-1;
        if(Math.pow(eqn[1],2)-4*eqn[0]*eqn[2]==0)
            solve=1;
        if(Math.pow(eqn[1],2)-4*eqn[0]*eqn[2] > 0)
            solve=2;
        return solve;
    }
}

10　　本题有个小技巧，我用的是“置0法”，把不符合要求的全部置0，2是素数，所以我们从下标为1的开始筛选，这个方法有点坑，因为你这样筛选可能会把本身给筛选掉，就需要错位筛选，比如筛选2的倍数，我们从3开始筛选，依次类推，因为求的是2~100的素数，所以因子只可能到50，定义循环的次数即可

public class Poten {
    public static void main(String[] args) {
        int a[] = new int[100];
        //int b[] =new int[99];
        int i,k,j,cout=0;
        for (i = 0; i < 99 ; i++) {
            a[i] = i+2;
        }
        for (int A : a)
            System.out.print(A+" ");
        System.out.println();
       /* System.out.println();
        k=0;
        System.out.println(a.length);
        for (i=0;i<a.length;i++) {
            if (a[i] % 2 != 0) {
                b[k] = a[i];
                k++;
            }
        }
        for (i=0;i<b.length;i++)
            System.out.print(b[i]+" ");*/
//          把每次结果都输出来显示。
        for (j = 2; j <=50 ; j++) {
            for (k = j-1 ; k<a.length ; k++) {
                if (a[k] % j == 0)
                    a[k]=0;
            }
            for (int A : a)
                System.out.print(A+" ");
            System.out.println();
        }

        for (i=0;i<a.length;i++){
            if (a[i]!=0)
                System.out.print(a[i]+" ");
        }
       // a[i] != ''
        //System.out.println(cout);
    }
}

11　　根据题目意思理解即可

import java.util.Arrays;

public class Poeleven {
    public static void main(String[] args) {
        int [] a={1,2,3,4};
        int [] b={1,2,3,4};

       System.out.println( equals(a,b));
       // System.out.println(a.equals(b));
    }
    public static boolean equals (int [] list1,int []  list2){
//        定义count的原因是把满足题目条件的结果进行加一
        int count=0;
        if(Arrays.equals(list1,list2)){
            for (int i = 0; i <list1.length ; i++) {
               if(list1[i]==list2[i])
                   count++;
            }
        }
//        满足条件的结果与数组长度相等则满足
        if (count==list1.length)
            return true;
        else
            return false;
    }

}

12　　本题用的 较简单的方法与第十题基本想法一致，每次循环一遍就把那个数“置0”

public class Potwleven {

    public static void main(String[] args) {
        int j=0,i=0;
        int a[]={1,2,3,4,5,6,7,8,9,10,11,12};
       //int t= s(a);
//        while循环的条件就是数组里面不为18的数大于1
        while (s(a)>1){
//            因为是12个数，则用%12来进行循环
            if (a[i%12]!=18)
                j++;
            if (j % 5 == 0)
                a[i%12]=18;
            i++;
        }
       // System.out.println(j);
        for (int k = 0; k <a.length ; k++) {
            if (a[k]!=18)
                System.out.println(a[k]);
        }
    }
    public static int s(int a[]){
        int count=0;
        for (int i = 0; i < a.length; i++) {
            if (a[i]!=18)
                count++;
        }
        return count;
    }
}

13　　本题的选牌次数纯属运气，因为有随机，根据题目意思定义一个二维数组来存放牌

import java.util.Random;

public class threeteen {
    public static void main(String[] args) {
        int [][]desk = new int[4][13];
        int count=1;
//        用来存放选牌的次数
        int cu=0;
        boolean flag =true;
        for (int i = 0; i <4 ; i++) {
            for (int j = 0; j < 13; j++) {
                desk[i][j]=count;
                count++;
            }
            count=1;
        }

        Random random =new Random();
        while (flag) {
            cu++;
            int r1 = random.nextInt(4);
            int r2 = random.nextInt(13);
            int a = desk[r1][r2];
            int b = desk[r1][r2];
            int c = desk[r1][r2];
            int d = desk[r1][r2];
            if (a+b+c+d==24)
                flag=false;

        }
        System.out.println(cu);
    }

   /* public static void main(String[] args) {
        int[] sum = new int[52];
        int[] a = new int[4];
        boolean flag = true;
        for (int i = 0; i < 52; i++) {
            sum[i] = i % 13 + 1;
        }
        for (int i = 0; i < sum.length; i++) {
            System.out.print(sum[i] + " ");
        }
        System.out.println();

        Random random = new Random();
        int r = random.nextInt(52);
        int n = sum.length;
        int cu = 0;
        while (flag) {
            for (int i = 0; i < 4; i++) {
                a[i] = sum[r];
                for (int j = r; j < n - 1; j++) {
                    sum[j] = sum[j + 1];
                }
                n--;
                for (int j = 0; j < n; j++) {
                    System.out.print(sum[j] + " ");
                }
                System.out.println();
            }

            System.out.println();
            if (a[0]+a[1]+a[2]+a[3]==24)
                flag=false;
          }*/


}

14　　本题就是求因子，每次求得的因子就让他进栈，知道最后一次进栈，最后再出栈，即可

import java.util.Scanner;

public class Pofourteen {
    private int[]elements;
    private int size=0;
    public static final int DEFAULT_CAPACITY = 10;

    public Pofourteen(){
        this(DEFAULT_CAPACITY);
    }
    public Pofourteen(int capacity){
        elements = new int[capacity];
    }
    //进栈
    public void push(int value){
        if(size >= elements.length){
            int []temp = new int[elements.length*2];
            System.arraycopy(elements,0,temp,0,elements.length);
            elements = temp;
        }
        elements[size++]=value;
    }
    //出栈
    public int pop() {
        return elements[--size];
    }

    public int peek() {
        return elements[size--];
    }
//  栈是否为空
    public boolean empty() {
        return size == 0;
    }

    public int getSize() {
        return size;
    }


    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int number = input.nextInt();
        Pofourteen stack = new Pofourteen();
        Pofourteen stack1 =new Pofourteen();
        int ans=0;
        int[] a = new int[20];
        while (number != 1) {
            for (int i = 2; i <= number; i++) {
                if (number % i == 0) {
                   // a[ans] = i;
                    stack.push(i);
                    ans++;
                    number /= i;
                    break;
                }
            }
        }
        while (!stack.empty()) {
            stack1.push(stack.pop());
         // System.out.print(stack1.pop() + " ");
        }
        //System.out.println();
        while (!stack1.empty()) {
           // stack1.push(stack.pop());
            System.out.print(stack1.pop() + " ");
        }
    }
}

15　　注意转置是什么意思，就是行列里面的元素互换

public class Pofifteen {
    public static void main(String[] args) {
        int [][]A= {{1,3,5},{-3,6,0},{13,-5,7},{-2,19,25}};
        int [][]B={{0,-1,2},{7,-1,6},{-6,13,2},{12,-8,-13}};
        System.out.println("A+B矩阵");
        jia(A,B);
        System.out.println("A-B矩阵");
        jian(A,B);
       // System.out.println(A[0].length);
      //  System.out.println(A.length);
        System.out.println("*********************");
        System.out.println("A的转置");
        zhuan(A);
    }
    public static void jia(int [][]a,int [][]b){
        int [][] add= new int[4][3];
        for (int i = 0; i < 4; i++) {
            for (int j = 0; j < 3; j++) {
                add [i][j] = a[i][j]+b[i][j];
                System.out.print(add [i][j]+" ");
            }
            System.out.println();
        }
    }
    public static void jian(int [][]a,int [][]b){
        int [][] add= new int[4][3];
        for (int i = 0; i < 4; i++) {
            for (int j = 0; j < 3; j++) {
                add [i][j] = a[i][j]-b[i][j];
                System.out.print(add [i][j]+" ");
            }
            System.out.println();
        }
    }
    public static void zhuan(int [][]a){
        int [][]AA=new int[3][4];
        for (int i = 0; i < a[0].length; i++) {
            for (int j = 0; j < a.length; j++) {
                AA[i][j]=a[j][i];
            }
        }
        for (int i = 0; i < a[0].length; i++) {
            for (int j = 0; j < a.length; j++) {
                System.out.print(AA[i][j]+" ");
            }
            System.out.println();
        }
    }
}

16　　把二维素组的下标存入数组即可

import java.util.Scanner;

public class Posixteen {
   public static int a1,a2;
    public static void main(String[] args) {
        System.out.print("请输入数组的行数和列数:");
        Scanner input = new Scanner(System.in);

        a1 = input.nextInt();
       a2 =input.nextInt();
       double [][]A=new double[a1][a2];
        for (int i = 0; i <a1 ; i++) {
            for (int j = 0; j <a2 ; j++) {
                A[i][j] = input.nextDouble();
            }
        }
        int C[]=locateLargest(A);
        System.out.println("最大数的位置是:"+"("+C[0]+","+C[1]+")");
    }
    public static int[] locateLargest(double [][] a){
       int n=0;
       int m=0;
       int c[]=new int[2];
        for (int i = 0; i <a1 ; i++) {
            for (int j = 0; j <a2 ; j++) {
             //   a[i][j] = input.nextDouble();
                if (a[i][j]>a[n][m]) {
                    c[0] = i;
                    c[1] = j;
                    n=i;
                    m=j;
                }
            }
        }
        return c;
    }
}

17　　本题水题，但是有点意思，根据题目的意思写即可

import java.util.Scanner;

public class Potwelve {
   /* public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int num = input.nextInt();
        int count = 1;
        int n=0,m=num/2;
        int temp1=0,temp2=0;
        int [][]A = new int[num][num];
        for (int i = 0; i <num*num; i++) {

            //    System.out.println(n+" "+m);

             //   if (A[n][m]==0){
                  //  A[n][m]=count;
            if (A[n][m]!=0) {
                n=++temp1;
                m=temp2;
            }
                A[n][m]=count;

                 //   System.out.println(n+" "+m+" "+A[n][m]);
                    count++;
                    temp1 = n;
                    temp2 =m;
                    n--;
                    m++;
                    if (n==-1)
                        n=num-1;
                    if (m==num)
                        m=0;
               // }
        }
        for (int i = 0; i <num; i++) {
            for (int j = 0; j <num; j++) {
                System.out.print(A[i][j]+" ");
            }
            System.out.println();
        }
    }*/
   public static void main(String[] args) {
       Scanner input =new Scanner(System.in);
       int num = input.nextInt();
       int [][]A=new int[num][num];

       int x=0,y=num/2;
       for (int i = 1; i <=num*num ; i++) {

           if (A[x][y]!=0) {
               //A[x][y] = i;
               x=(x+2)%num;
             //  y=(y+1)%num;
//               保存原来位置的y
               y=(y+num-1)%num;
           }
          A[x][y]=i;
           x=(x+num-1)%num;
           y=(y+1)%num;
       }
       for (int i = 0; i < num; i++) {
           for (int j = 0; j < num; j++) {
               System.out.print(A[i][j]+" ");
           }
           System.out.println();
       }
   }
}