Day32 List

1. 用 List 存储一些字符串，去除里面重复的字符串，只保留一个。

public class Test2List {

   public static void main(String[] args) {
       List<String> list = new ArrayList<>();
       String[] strings = {"xjn", "wmz", "chq", "wmz", "wsm", "lyh", "yzg", "wmz"};
       for (String string : strings) {
           if (!list.contains(string)) {
               list.add(string);
           }
       }
       System.out.println(list);
   }
}

2. 生成20个 1-20 的随机整数，把其中不重复的整数存入 List 集合中（相同的整数只存一个）。

public class Test3List {

   public static void main(String[] args) {
       List<Integer> list = new ArrayList<>();
       for (int i = 0; i < 20; i++) {
           Random random = new Random();
           int value = random.nextInt(20) + 1;
           if (!list.contains(value)) {
               list.add(value);
           }
       }
       System.out.println(list);
   }
}

3. 假设某个程序会进行一系列入栈和出栈的混合栈操作。入栈操作会将整数 0 到 9 按顺序压入栈；

   出栈操作会打印除返回值。下面哪些序列是不可能产生的？

   a. 4 3 2 1 0 9 8 7 6 5

   b. 4 6 8 7 5 3 2 9 0 1

   c. 2 5 6 7 4 8 9 3 1 0

   d. 4 3 2 1 0 5 6 7 8 9

   e. 1 2 3 4 5 6 9 8 7 0

   f. 0 4 6 5 3 8 1 7 2 9

   g. 1 4 7 9 8 6 5 3 0 2

   h. 2 1 4 3 6 5 8 7 9 0

//(网上的代码，原本有部分不适用，已修改)
public class Test4 {

   public static void main(String[] args) {
       int[] a = {4, 3, 2, 1, 0, 9, 8, 7, 6, 5};
       int[] b = {4, 6, 8, 7, 5, 3, 2, 9, 0, 1};
       int[] c = {2, 5, 6, 7, 4, 8, 9, 3, 1, 0};
       int[] d = {4, 3, 2, 1, 0, 5, 6, 7, 8, 9};
       int[] e = {1, 2, 3, 4, 5, 6, 9, 8, 7, 0};
       int[] f = {0, 4, 6, 5, 3, 8, 1, 7, 2, 9};
       int[] g = {1, 4, 7, 9, 8, 6, 5, 3, 0, 2};
       int[] h = {2, 1, 4, 3, 6, 5, 8, 7, 9, 0};
       int[][] ints = new int[8][];
       ints[0] = a;
       ints[1] = b;
       ints[2] = c;
       ints[3] = d;
       ints[4] = e;
       ints[5] = f;
       ints[6] = g;
       ints[7] = h;

       for (int[] anInt : ints) {
           System.out.println(Arrays.toString(anInt));
           System.out.println(isTrue(anInt));
       }
   }

   public static boolean isTrue(int[] arr) {
       boolean[] marked = new boolean[arr.length];
       for (int i = 0; i < arr.length; i++) {
           if (marked[i]) {
               continue;
           }
           int cut = arr[i];
           marked[i] = true;
           for (int j = i + 1; j < arr.length; j++) {
               if (arr[i] > arr[j]) {
                   if (arr[j] > cut) {
                       return false;
                   } else {
                       cut = arr[j];
                   }
                   marked[j] = true;
               }
           }
       }
       return true;
   }
}