day14- 数组

数组

数组类

Array 类：

Array.toString(a): 输出数组，直接print（a）是输出其hash cold值

1 int[] a = {1,2,3,4,45,67,9989,45};
2  System.out.println(a);
3  //直接打印a是 hashcode  [I@1b6d3586
4  printarr(a);
5  System.out.println();
6  System.out.println(Arrays.toString(a));

写一个数组遍历函数：

 1 public static void printarr(int[] a ){
 2      for (int i = 0; i < a.length; i++) {
 3          if(i==0){
 4              System.out.print("["+a[i]+", ");
 5          } else if (i== a.length-1) {
 6              System.out.print(a[i]+"]");
 7  
 8          }else {
 9              System.out.print(a[i]+", ");
10          }
11  
12  
13      }
14  }

排序函数：sort

1 int[] a = {1,2,3,4,45,67,9989,45};
2  Arrays.sort(a);
3  System.out.println(Arrays.toString(a));

冒泡排序：

 1 public static void main(String[] args) {
 2  
 3      int[] a = {1,2,3,4,45,67,9989,45};
 4      sort(a);
 5      System.out.println(Arrays.toString(a));
 6  }
 7  
 8  //冒泡排序
 9  //1.比较数组中相邻的两个元素大小
10  //2. 每次比较选择一个最大或者最小的数字
11  //3. 下一次可以少一次比较排序
12  public static int[] sort(int[] array ){
13      int temp = 0;
14      //外层循环，判断要走多少次
15      for (int i = 0; i < array.length-1; i++) {
16          //内层循环，交换比较位置
17          for (int j = 0; j < array.length - 1 - i; j++) {
18              if(array[j+1]>array[j]){
19                 temp=array[j];
20                 array[j] = array[j+1];
21                 array[j+1] = temp;
22              }
23          }
24  
25      }
26      return array;
27  }

稀疏数组

数组中大部分数为0，存储方便以稀疏数组的形式存储

 1 //1. 创建一个二维数组11*11， 0：没有棋子 1：黑棋 2:白棋
 2  public static void main(String[] args) {
 3      int[][] array1 = new int[11][11];
 4      array1[1][2] = 1;
 5      array1[2][3] = 2;
 6  
 7      for(int[] ints:array1){
 8          for (int an :ints){
 9              System.out.print(an +"\t");
10          }
11          System.out.println();
12      }
13      //转换为稀疏数组
14      //获取有效值的个数
15      int sum = 0;
16      for (int i = 0; i < 11; i++) {
17          for (int j = 0; j < 11; j++) {
18              if(array1[i][j]!=0){
19                  sum++;
20              }
21          }
22      }
23      System.out.println(sum);
24      int[][] array2 = new int[sum+1][3];
25      array2[0][0] = array1.length;
26      array2[0][1] = array1.length;
27      array2[0][2] = sum;
28      int count = 0;
29      for (int i = 0; i < array1.length; i++) {
30          for (int j = 0; j < array1[i].length; j++) {
31  
32              if(array1[i][j]!= 0 ){
33                  count++;
34                  array2[count][0] = i;
35                  array2[count][1] = j;
36                  array2[count][2] = array1[i][j];
37              }
38          }
39      }
40      System.out.println("稀疏数组");
41      for (int i = 0; i < array2.length; i++) {
42          System.out.println(array2[i][0]+"\t"+array2[i][1]+"\t"+array2[i][2]+"\t");
43      }
44  
45  
46  
47      //还原稀疏数组
48      int[][] array3 = new int[array2[0][0]][array2[0][1]];
49      for (int i = 1; i < array2.length; i++) {
50          array3[array2[i][0]][array2[i][1]] = array2[i][2];
51  
52      }
53      for(int[] ints:array3){
54          for (int an :ints){
55              System.out.print(an +"\t");
56          }
57          System.out.println();
58      }
59  
60  }