JAVA学习第五课（排序+二分查找+查表法）

PS:算法是不分语言的

排序：

1.抽取 

2.交换位置

 import javax.swing.text.DefaultEditorKit.InsertBreakAction;

 import org.omg.CosNaming.NamingContextExtPackage.AddressHelper;


 public class Main
 {
     public static void main(String[] args)
     {
     //  int[] b = new int[]{1,2,3,4,5};同下

         int b[] = {1,2,1,3,4,7,8,9,4,1,2,5,6,7,4,5,1,2,3,6};//同上

         bubblesort(b);
         System.out.println("冒泡排序结果如下:");
         print(b);

         int c[] = {1,2,1,3,4,7,8,9,4,1,2,5,6,7,4,5,1,2,3,6};
         seletsort(c);
         System.out.println("选择排序结果如下:");
         print(c);

         int d[] = {1,2,1,3,4,7,8,9,4,1,2,5,6,7,4,5,1,2,3,6};
         Insersort(d);
         System.out.println("\n插入排序结果如下:");
         print(d);
     }
     static void Insersort(int b[])
     {
         int len = b.length;
         for(int i = 1;i<len;i++)
         {
             if(b[i]<b[i-1])
             {
                 int t = b[i],j;
                 b[i] = b[i-1];
                 for(j = i-2;i>=0 && b[j] > t;j--)
                 {
                     b[j+1] = b[j];
                 }
                 b[j+1] = t;
             }
         }
     }
     static void swap(int x,int y,int[] b)
     {
         int t = b[x];
         b[x] = b[y];
         b[y] = t;
     }
     /*static void swap(int a,int b)不要写成这种方式，只是单纯的交换了两个数，
      *                              但是b数组里这两个数并没有交换
     {
         int t = a;a = b;b = t;
     }*/
     static void bubblesort(int[] b)
     {
         int len = b.length;
         for(int i = 0;i<len;i++)
         {
             for(int j = 0;j<len-i-1;j++)
             {
                 if(b[j]>b[j+1])
                 {
                     swap(j, j+1,b);
                 }
             }
         }

     }
     static void seletsort(int a[])
     {
         int len = a.length;
         for(int i = 0;i<len-1;i++)
         {
             for(int j = i+1;j<len;j++)
             {
                 if(a[i] > a[j])
                 {
                     swap(i, i+1,a);
                 }
             }
         }
     }
     static void print(int b[])
     {
         for(int i = 0;i<b.length;i++)
             System.out.println("b["+i+"] = "+b[i]);
     }
 }

 import javax.swing.text.DefaultEditorKit.InsertBreakAction;

 import org.omg.CosNaming.NamingContextExtPackage.AddressHelper;


 public class Main
 {
     public static void main(String[] args)
     {
     //  int[] b = new int[]{1,2,3,4,5};同下

         Scanner cin = new Scanner(System.in);

         int b[] = new int[11];
         for(int i = 0;i<11;i++)
         {
             b[i] = cin.nextInt();
         }
         bubblesort(b);
         System.out.println("冒泡排序结果如下:");
         print(b);
         System.out.print("请输入你要查找的值：");
         int n;
         n = cin.nextInt();

         boolean flag = B_search(n,b);

         if(flag==true)
             System.out.println("YES");
         else
             System.out.println("NO");

         cin.close();
     }

     static void swap(int x,int y,int[] b)
     {
         int t = b[x];
         b[x] = b[y];
         b[y] = t;
     }
     static boolean B_search(int n,int b[])
     {
         int low = 0,high = b.length-1;

         while(low<=high)
         {
             int mid = ( low + high ) / 2;
             if(b[mid] == n)
             {
                 return true;
             }
             else if(b[mid] > n)
             {
                 high = mid - 1;
             }
             else
             {
                 low = mid + 1;
             }
         }
         return false;
     }
     static void bubblesort(int[] b)
     {
         int len = b.length;
         for(int i = 0;i<len;i++)
         {
             for(int j = 0;j<len-i-1;j++)
             {
                 if(b[j]>b[j+1])
                 {
                     swap(j, j+1,b);
                 }
             }
         }

     }
     static void print(int b[])
     {
         for(int i = 0;i<b.length;i++)
             System.out.println("b["+i+"] = "+b[i]);
     }
 }

二分查找：面试题
 
给个一个有序数组，如果往这个数组中存储一个元素，并保证这个数组还是有序的，那么这个元素的存储的角标如何获取

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


 import javax.swing.text.DefaultEditorKit.InsertBreakAction;


 import org.omg.CosNaming.NamingContextExtPackage.AddressHelper;




 public class Main
 {
     public static void main(String[] args)
     {
     //  int[] b = new int[]{1,2,3,4,5};同下

         Scanner cin = new Scanner(System.in);

         int b[] = new int[11];
         for(int i = 0;i<11;i++)
         {
             b[i] = cin.nextInt();
         }
         bubblesort(b);
         System.out.println("冒泡排序结果如下:");
         print(b);
         System.out.print("请输入你要查找的值：");
         int n;
         n = cin.nextInt();
         System.out.println("手写二分查找:");
         int flag = B_search(n,b);

         System.out.println("下标为：\t"+flag);
             int wz = cin.nextInt();
         int indx = Arrays.binarySearch(b, wz);//返回的是个：负的插入点下标再减1
         //返回负数，代表着不存在，如果我往里放这个元素，插入点在哪，负数指的是：负的插入点下标，再-1
         //返回正数，代表着其下标
         /*为什么要减1？
          * 如果要插入的元素比数组元素的第一个还小，不减1，会返回0，而返回0，是不是就这个数代表着不存在，故要减1
          * */
         System.out.println("调用二分查找:");
         System.out.println("下标为：\t"+indx);
         cin.close();
     }

     static void swap(int x,int y,int[] b)
     {
         int t = b[x];
         b[x] = b[y];
         b[y] = t;
     }
     static int B_search(int n,int b[])
     {
         int low = 0,high = b.length-1;

         while(low<=high)
         {
             int mid = ( low + high ) / 2;
             if(b[mid] == n)
             {
                 return mid;
             }
             else if(b[mid] > n)
             {
                 high = mid - 1;
             }
             else
             {
                 low = mid + 1;
             }
         }
         return low;
     }
     static void bubblesort(int[] b)
     {
         int len = b.length;
         for(int i = 0;i<len;i++)
         {
             for(int j = 0;j<len-i-1;j++)
             {
                 if(b[j]>b[j+1])
                 {
                     swap(j, j+1,b);
                 }
             }
         }

     }
     static void print(int b[])
     {
         for(int i = 0;i<b.length;i++)
             System.out.println("b["+i+"] = "+b[i]);
     }
 }

查表法

 import java.util.Scanner;


 public class Main
 {
     /*
      * 使用查表法

      */

     /*查表法的应用：
      * 有规律的，就可以使用查表法
      * */
     public static void main(String[] args)
     {
         Scanner cin = new Scanner(System.in);

         {
             int x = cin.nextInt();
             /*
              * 查询星期
              * */
             System.out.println(Find(x));

             /*
              * 查询月份
              * */
             int y = cin.nextInt();
             System.out.println(Findd(y));
             cin.close();

         }

     }
     public  static String Find(int x)
     {
         if(x>7 || x<0)
         {
             return "输入错误";
         }
         String[] week = {"星期一 = Monday","星期二 = Tuesday","星期三 = Wednesday","星期四 = Thurseday","星期五 = Friday","星期六 = Saturday","星期天 = Sunday"};
         return week[x-1];
     }
     public  static String Findd(int x)
     {
         if(x>12 || x<0)
         {
             return "输入错误";
         }
         String[] mon = {"一月 = January","二月  = Febary","三月 = March","四月 = April","五月 = May"
                 ,"六月 = June","七月 = July","八月 = August","九月   = Spetember","十月  = October","十一月  = November","十二月  = December"};
         return mon[x-1];
     }

 }