数组应用

1.数组反转

import java.util.Arrays;

public class ArrayReverse {
    public static void main(String[] args){
        int[] arr ={1,2,3,4,5,6,7,8,9};
        reverse(arr);
    }
    public static void reverse(int[] arr){
        for(int i=0;i<arr.length/2;i++){
            int temp = arr[i];
            arr[i] =arr[arr.length-1-i];
            arr[arr.length-1-i]=temp;
        }
        System.out.println(Arrays.toString(arr));
    }
}

2.求最值

class  ZuiZhi
 {
     public static void main(String[] args) 
     {
         int[] a={2,92,34,54,28};
         minMethod(a);
         maxMethod(a);
     }
     public static void minMethod(int[] a)
     {
         int min=a[0];//不能初始化为0 数组中可能有负数
         for (int i=0;i<a.length;i++ )
         {
             if(a[i]<min)
                 min=a[i];
         }
         System.out.println("数组内最小的元素是："+min);
     }
     public static void maxMethod(int[] a)
     {
         int max=a[0];//不能初始化为0 数组中可能有负数
         for (int i=0;i<a.length;i++ )
         {
             if(a[i]>max)
                 max=a[i];
         }
         System.out.println("数组内最大的元素是："+max);
     }
 
 }

3.折半查找

/*
 折半查找：
 3 5 7 9 10 14 
 min=0 max=length-1 mid=(max+min)/2
 */
 class BinarySearch 
 {
     public static void main(String[] args) 
     {
         int[] a={3,5,7,9,10,14};
         int index=binarySearch_1(a,7);
         System.out.println(index);
         index=binarySearch_2(a,14);
         System.out.println(index);    
     }
     public static int binarySearch_1(int[] a,int key)
     {
         int min=0,mid,max=a.length-1;
         mid=(min+max)/2;
         while (key!=a[mid])
         {
             if(a[mid]>key)
             {
                 max=mid-1;
             }
             else  if (a[mid]<key)
             {
                 min=mid+1;
             }
             if (max<min)
                 return -1;
             mid=(min+max)/2;
 
         }
         return mid;
     }
     public static int binarySearch_2(int[] a,int key)
     {
         int min=0,max=a.length-1,mid;
         while (min<=max)
         {
             mid =(max+min)>>1;
             if(a[mid]>key)
             {
                 max=mid-1;
             }
             else  if (a[mid]<key)
             {
                 min=mid+1;
             }
             else 
                 return mid;
         }
         return -1;
     }
     
 }