java - 当尝试对相同的值进行两次计数时，循环不正确且超出 HashMap 的范围

Question

下面的代码接受用户输入(int 值)，然后查找重复、偶数、数量。

2 个问题:

1. The 1st even number gets printed 3 times, if in your input you have 2 7 19 8 it will look like 2, 2, 2, 8 . Why I am unable to
   understand.
2. The hashmap part where I put list.get(intNum)+1 to count a value twice gives out of bound. Without that it runs. How can I count a number twice?

提前致谢。

public class Various {

    static Scanner userinput= new Scanner(System.in);
    static int nums;
    static int big;//will be used to find bug number in array
    public static void main(String[] args) {

        List<Integer> list= new ArrayList<>();//for all numbers
        List<Integer> listEven= new ArrayList<>(); //just for evens
        Map<Integer,Integer> hmap= new HashMap<Integer,Integer>(); //number count

        System.out.println("Enter some numbers: ");
        nums=userinput.nextInt();
        big=nums;
        int evenNumber;

        list.add(nums);

        while(userinput.hasNextInt()){
            nums=userinput.nextInt();

            //below part of the code finds biggest value
            if(nums>big){
                big=nums;
            }
            //Above part of the code finds biggest value

            list.add(nums);

            //below part of the code finds/prints duplicate value
            for(int i=0;i<list.size()-1;i++){           
                for(int j=i+1;j<list.size();j++){
                    if(list.get(i)==list.get(j)){
                        System.out.println("Duplicate " + list.get(j));
                    }
                }
                //Above part of the code finds/prints duplicate value
            }
            //below part of the code finds even numbers
            for(int i=0;i<list.size();i++){
                //for loop will start from 0 till user input            
                if(list.get(i)%2==0){
                    //if any of those i values%2=0 those will be Even and I will capture those
                    listEven.add(list.get(i));
                }
                //Above part of the code finds even numbers
            }
            //below part of the code finds number occurrence count          
            for(Integer intNum: list){
                if(!(hmap).containsKey(intNum)){
                    hmap.put(intNum, 1);
                }else{
                    //below part to take care if a number comes twice i add 1 more(+1)
                    hmap.put(intNum, list.get(intNum)+1);
                }   
                //Above part of the code finds number occurrence count  
            }
        }
        System.out.println("Values are " + list);
        System.out.println("Biggest value " + big);
        System.out.println("Even numbers " + listEven);
        System.out.println("Numbers in list and occurance " + hmap);
    }
}

Answer 1

问题A:

在您的代码中，您有一个 while 循环来检查数字，但每次用户输入数字时，您都会循环遍历数字列表并检查偶数。

最合乎逻辑的方法是更改​​代码，以便在用户输入所有号码后检查偶数。或者您可以添加这个，这是一个较小的解决方案，但它会起作用:

<小时/>

listEven.add(list.get(i));

将上面的代码更改为下面的代码。

if (!listEven.contains(list.get(i))) {
    listEven.add(list.get(i));
}

问题B:

错误在于这段代码:

// below part of the code finds number occurrence count
for (Integer intNum : list) {
    if (!(hmap).containsKey(intNum)) {
        hmap.put(intNum, 1);
    } else {
        // below part to take care if a number comes twice i add 1
        // more(+1)
        hmap.put(intNum, list.get(intNum) + 1);
    }
    // Above part of the code finds number occurrence count
}

<小时/>

您正在尝试执行list.get(intNum)，但是方法get需要索引，而不需要 您要查找的值。我认为您的意思是输入 hmap.get(intNum) 而不是 list.get(intNum)，这将正确更新计数。