java数组练习

上一次数组感觉有个重点没写上当数组相等  当：定义`arr1 = arr2;`

此时两数组完全相等因为传输了首地址相等（指针）

这一波主要也就是锻炼思维，后面Arrays工具直接解决

数组基本操作

求和、平均数、找最大值、找最小值

package com.lys.demo2;

import java.util.Scanner;

public class AlgorithmArray {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter the size of array: ");
        int n = sc.nextInt();
        int[] arr1 = new int[n];
        System.out.println("Enter the elements of array: ");
        for (int i = 0; i < n; i++) {
            arr1[i]=sc.nextInt();//输入数组
        }
        //GetMax
        int max=arr1[0];
        for (int i = 1; i < n; i++) {
            if (max<arr1[i]) {
                max=arr1[i];
            }
        }
        System.out.println("The maximum value is "+max);
        //GetMin
        int min=arr1[0];
        for (int i = 1; i < n; i++) {
            if (min>arr1[i]) {
                min=arr1[i];
            }
        }
        System.out.println("The minimum value is "+min);
        //GetSum
        int sum=0;
        for (int i = 0; i < n; i++) {
            sum+=arr1[i];
        }
        System.out.println("The sum of all elements is "+sum);
        //GetAverage
        double average=sum/n;
        System.out.println("The average of all elements is "+average);
    }
}

数组反转的两种方法

其实细看也差不多（其实就是一摸一样，格式有点不同）

package com.lys.demo2;
//数组反转
public class ArrayReversalTest {
    public static void main(String[] args) {
        int[] arr = new int[]{1,2,3,4,5,6,7,8,9,10};
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]+" ");
        }
        System.out.println();
        int n = 0,m = arr.length-1;
        for(int i = 0 ; i < arr.length/2 ; i++){
            int temp = arr[n];
            arr[n] = arr[m];
            arr[m] = temp;
            n++;
            m--;
        }
        for(int i = 0 ; i < arr.length ; i++){
            System.out.print(arr[i]+" ");
        }
        System.out.println();
        //方法二
        for(int i = 0,j = arr.length-1 ; i < arr.length/2 ; i++,j--){
            int temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
        for(int i = 0 ; i < arr.length ; i++){
            System.out.print(arr[i]+" ");
        }
    }
}

遍历数组

输出所有扑克牌（最后一步for只是为了美观）

package com.lys.demo2;

public class PlayingCard {
    public static void main(String[] args) {
        String[] suits = {"Clubs", "Diamonds", "Hearts", "Spades"};
        String[] ranks = {"1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K"};
        String[] indexs = new String[(suits.length * ranks.length)+2];
        indexs[indexs.length-2] = "big jocker   ";
        indexs[indexs.length-1] = "small jocker";
        int n = 0;
        for (int i = 0; i < suits.length; i++){
            for (int j = 0; j < ranks.length; j++){
                indexs[n++] = suits[i] + ranks[j];
            }
        }
        for (int i = 0; i < indexs.length; i++){
            if ((i)%13==0){
                System.out.println();
            }
            System.out.print(indexs[i]);
        }

    }
}

数组查找（可以去看黑马的c语言，每一个方法都是一个视频）

1.遍历查找

（函数的使用方法还真被我猜对了，和c也差不多）

package com.lys.demo2;

import java.util.Scanner;

public class LinearSearch {
    public static int linearSearch(int[] arr, int key) {
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] == key) {
                return i;
            }
        }
        return -1;
    }
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] arr = new int[]{1,2,3,4,5,6,7,8,9};
        System.out.println("请输入你想要查找的数字");
        int key = sc.nextInt();
        int result = linearSearch(arr, key);
        System.out.println("这个数字在这个数组中的索引是" + result);

    }
}

2.二分查找

package com.lys.demo2;

import java.util.Scanner;

public class BinarySearch {
    public static int binarySearch(int[] arr, int target) {
        int low = 0;
        int high = arr.length - 1;
        while (low <= high) {
            int mid = (low + high) / 2;
            if (arr[mid] == target) {
                return mid;
            }
            if (arr[mid] < target) {
                low = mid + 1;
            }
            else  {
                high = mid - 1;
            }
        }
        return -1;
    }
    public static void main(String[] args) {
        int[] arr = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        Scanner sc = new Scanner(System.in);
        int target = sc.nextInt();
        System.out.println(binarySearch(arr, target));
    }
}

数组排序

1.冒泡排序

package com.lys.demo2;

public class BubbleSort {
    public static void bubbleSort(int[] arr){
        for(int i=0;i<arr.length-1;i++){
            for(int j=0;j<arr.length-i-1;j++){
                if(arr[j]>arr[j+1]){
                    int temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                }
            }
        }
    }
    public static void main(String[] args) {
        int[] arr = new int[]{4,7,3,5,2,6,1,9};
        bubbleSort(arr);
        for(int i=0;i<arr.length;i++){
            System.out.print(arr[i]+" ");
        }
    }
}

2.选择排序（更好理解，难度也不大）

package com.lys.demo2;

public class SelectSort {
    public static void selectSort(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            for (int j = i+1; j < arr.length; j++) {
                if(arr[i] > arr[j]) {
                    int temp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = temp;
                }
            }
        }
    }
    public static void main(String[] args) {
        int[] arr = new int[]{7,3,5,2,6,1,8,4};
        selectSort(arr);
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i]+" ");
        }
    }
}

ok也是开始面向对象了  争取在期中之前学完javase  直接冲