数组练习 后续补充

1、数组平均值

    public static double avg(int[] array){
        int sum = 0;
        for (int i = 0; i < array.length; i++) {
            sum += array[i];
        }
        return sum*(1.0) / array.length;
    }

    public static void main(String[] args) {
        int[] array = {5,65,21,34,79,63};
        System.out.println(avg(array));
    }
    运行代码:
    44.5
    Process finished with exit code 0

2、查找数组中指定元素(顺序查找)

   public static int key(int[] array,int key){
       for (int i = 0; i < array.length; i++) {
           if (array[i]==key){
               return i;
           }
       }
       return -1;
   }

    public static void main(String[] args) {
        int[] array = {1,2,3,4,5,6};
        int index = key(array,5);
        if (index == -1){
            System.out.println("数组中没有你要找的关键字！");
        }else {
            System.out.println("找到了你要的关键字，下标为:"+index);
        }
    }
    运行代码:
    找到了你要的关键字，下标为:4
    Process finished with exit code 0

3、二分查找

    public static int two(int[] array,int key) {
        int left = 0;
        int right = array.length - 1;
        while (left <= right) {
            int mid = (left + right) / 2;
            if (array[mid] > key) {
                right = mid - 1;
            } else if (array[mid] < key) {
                left = mid + 1;
            } else {
                return mid;
            }
        }
        return -1;
    }
    public static void main(String[] args) {
        int[] array = {1,2,3,14,5};
        Arrays.sort(array);
        System.out.println("排序之后的数组:"+Arrays.toString(array));
        int index = two(array,5);
        if (index == -1){
            System.out.println("数组中没有你要找的关键字！");
        }else {
            System.out.println("找到了你要的关键字，下标为:"+index);
        }
    }
    运行代码:
    排序之后的数组:[1, 2, 3, 5, 14]
    找到了你要的关键字，下标为:3
    Process finished with exit code 0

4、冒泡排序

 public static void bubbleSort(int[]  array){
        for (int i = 0; i < array.length-1; i++) {
            for (int j = 0; j < array.length-1-i; j++) {
                if (array[j]>array[j+1]){
                    int tmp = array[j];
                    array[j]=array[j+1];
                    array[j+1] = tmp;
                }
            }
        }
    }

    public static void main(String[] args) {
        int[] array = {1,2,31,14,5};
        System.out.println("排序之前，数组为:"+ Arrays.toString(array));
        bubbleSort(array);
        System.out.println("排序之后，数组为:"+ Arrays.toString(array));
    }
    运行代码:
    排序之前，数组为:[1, 2, 31, 14, 5]
    排序之后，数组为:[1, 2, 5, 14, 31]
    Process finished with exit code 0

优化一下：不变化就结束

 public static void bubbleSort(int[]  array){
        for (int i = 0; i < array.length-1; i++) {
            boolean flg = false;
            for (int j = 0; j < array.length-1-i; j++) {
                if (array[j]>array[j+1]){
                    int tmp = array[j];
                    array[j]=array[j+1];
                    array[j+1] = tmp;
                    flg = true;
                }
            }
            if (flg == false) break;;
        }
    }

    public static void main(String[] args) {
        int[] array = {1,2,31,14,5};
        System.out.println("排序之前，数组为:"+ Arrays.toString(array));
        bubbleSort(array);
        System.out.println("排序之后，数组为:"+ Arrays.toString(array));
    }
    排序之前，数组为:[1, 2, 31, 14, 5]
    排序之后，数组为:[1, 2, 5, 14, 31]
    Process finished with exit code 0

5、数据逆置

public static void main(String[] args) {
        int[] array = {1,2,31,14,5};
        System.out.println("逆置之前，数组为:"+ Arrays.toString(array));
        reverse(array);
        System.out.println("逆置之后，数组为:"+ Arrays.toString(array));
    }

    public static void reverse(int[] array){
        int left = 0;
        int right = array.length-1;
        int tmp = 0;
        while (left<right){
            tmp = array[left];
            array[left] = array[right];
            array[right]= tmp;
            left++;
            right--;
        }
    }
    逆置之前，数组为:[1, 2, 31, 14, 5]
    逆置之后，数组为:[5, 14, 31, 2, 1]
    Process finished with exit code 0

6、二维数组

优化一下：不变化就结束定义

public static void main(String[] args) {
        //手动加花括号
        int[][] array = {
   {1,2,3},{4,5,6}};
        //也不能填数字
        int[][] array2 = new int[][]{
   {1,2,3},{4,5,6}};

        //不晓得数值情况  默认0
        int[][] array3 = new int[2][3];
    }

优化一下：不变化就结束打印: 很麻烦

 public static void main(String[] args) {
        int[][] array = {
   {1,2,3},{4,5,6}};
        for (int i = 0; i < 2; i++) {
            for (int j = 0; j < 3; j++) {
                System.out.print(array[i][j]+" ");
            }
            System.out.println();
        }
    }
    运行代码:
    1 2 3 
    4 5 6 
    Process finished with exit code 0

优化一下：不变化就结束万能打印:

public static void main(String[] args) {
        int[][] array = {
   {1,2,3},{4,5,6}};
        for (int i = 0; i < array.length; i++) {
            for (int j = 0; j < array[i].length; j++) {
                System.out.print(array[i][j]+" ");
            }
            System.out.println();
        }
    }
     运行代码:
    1 2 3 
    4 5 6 
    Process finished with exit code 0

优化一下：不变化就结束二维数组示意图:

优化一下：不变化就结束使用foreach进行打印:

System.out.println("使用foreach进行打印");
        for (int[] tmp:array) {
            System.out.println(tmp);
            for (int x: tmp) {
                System.out.print(x+" ");
            }
            System.out.println();
        }
        运行代码:
        使用foreach进行打印
        [[email protected]
        1 2 3 
        [[email protected]
        4 5 6 
        Process finished with exit code 0

优化一下：不变化就结束使用toString方法进行打印:

System.out.println("使用toString方法进行打印");
        //深度打印方法Arrays.deepToString()
        System.out.println(Arrays.deepToString(array));
        运行代码:
        使用toString方法进行打印
        [[1, 2, 3], [4, 5, 6]]
        Process finished with exit code 0