如何在数组/数组列表中存储和读取扫描仪输入？

Question

我正在尝试编写一个程序来打印出存储在ArrayList 中的第三大数字。我尝试对其进行排序，然后将列表反转为并使用 get() 方法来获取第三高数字的索引。但它没有考虑前 3 个插槽中是否存在重复。

如何遍历arraylist得到第三个highs值？

到目前为止我做了什么。

import java.util.*;

public class third {
    public static void main(String[] args) {
       

        ArrayList<Integer> numbers = new ArrayList<>(); //creating an array object
        Scanner scan = new Scanner(System.in); // scanner to read user input

        
        // print statement to get input
        System.out.print("Enter any amount of numbers: "); 
        int i = 0;
        while (scan.hasNextInt()) {// while there is an hasnext has an int                
            numbers.add(scan.nextInt()); //adding input(numbers) to an arraylist
            i++; //increment by 1                     
        } 
        scan.close(); // close the scanner if the user doesnt enter a number.
        
        System.out.println("you entered: " + numbers);
        System.out.println("The largest number you entered is: " + Collections.max(numbers));//print largest number
        System.out.println("The smallest number you entered is: " + Collections.min(numbers));//print smallest number

        Collections.sort(numbers); //sorting the numbers from lowest to highest
        System.out.println("Sorted: " + numbers); //print sorted numbers

        Collections.reverse(numbers); //reverse the order to use to get the third highest value
        System.out.println("Highest to lowest: " + numbers);
        System.out.println("Third highest number is:" + numbers.get(2));//get the third index of the sorted ArrayList       
        }
}

Answer 1

最后需要一个循环来丢弃重复项并找到准确的第三大数字。正如我所做的那样。

import java.util.*;

public class third {
public static void main(String[] args) {
   

    ArrayList<Integer> numbers = new ArrayList<>(); //creating an array object
    Scanner scan = new Scanner(System.in); // scanner to read user input

    
    // print statement to get input
    System.out.print("Enter any amount of numbers: "); 
    int i = 0;
    while (scan.hasNextInt()) {// while there is an hasnext has an int                
        numbers.add(scan.nextInt()); //adding input(numbers) to an arraylist
        i++; //increment by 1                     
    } 
    scan.close(); // close the scanner if the user doesnt enter a number.
    
    System.out.println("you entered: " + numbers);
    System.out.println("The largest number you entered is: " + Collections.max(numbers));//print largest number
    System.out.println("The smallest number you entered is: " + Collections.min(numbers));//print smallest number

    Collections.sort(numbers); //sorting the numbers from lowest to highest
    System.out.println("Sorted: " + numbers); //print sorted numbers

    Collections.reverse(numbers); //reverse the order to use to get the third 
    highest value
    System.out.println("Highest to lowest: " + numbers);
    int counter=0; // To find distinct number 
    for(int i=numbers.size()-1 ; i>=0 ; i--){ // Another loop to by pass 
    //duplicates
    if(numbers.get(i)!=numbers.get(i-1)){
    counter++;
    }
    if(counter==2){      // third highest
      System.out.println("Third highest number is:" + numbers.get(i));//get
    //third index of the sorted ArrayList 
    break;
    }
         
    }
    }

Answer 2

将arraylist 值传递给hashmap。或者将值存储在哈希图中。 Hashmap 包含无重复项。之后反转集合并像你一样做。

Answer 3

为了找到第三大元素，只需从您的数字列表中创建一个SortedSet。如果该集合至少包含三个元素，那么倒数第三个元素就是您想要的。为了获得倒数第三个元素，请将SortedSet 转换为数组。请参见下面的代码。请注意，SortedSet 是由类TreeSet 实现的接口。

SortedSet<Integer> ss = new TreeSet<>(numbers);
if (ss.size() > 2) {
    System.out.println("Third highest number is:" + ss.toArray(new Integer[0])[ss.size() - 3]);//get the third index of the sorted ArrayList
}

Answer 4

您使用 SortedSet 对重复项进行排序和删除，因此您可以使用（草稿，不检查）而不是 Collections.sort(numbers);：

 SortedSet<Integer> numbersSet = new TreeSet<>(numbers );
 numbers = new ArrayList<>(numbersSet);
 Collections.reverse(numbers);        

 Collections.reverse(numbers); //reverse the order to use to get the third highest value
 System.out.println("Highest to lowest: " + numbers);
 System.out.println("Third highest number is:" + numbers.length() > 2? numbers.get(2): "not found");//get the third index of the sorted ArrayList