排序字符的频率 [英] Sorting frequency of chars

问题描述

我刚刚制作了一个计算字符串中字符频率的算法。令我困惑的是如何对频率进行排序，以便在顶部列出具有最大出现次数的字符，在底部列出最少的字符。

I just made an algorithm that counts the frequency of chars in a String. What I am confused about is how to sort the frequency so the character with the greatest number of occurences is listed at the top, and the least at the bottom.

首先，我尝试使用另一个变量'fc'（对于频率计数器）与我原来的计数器变量'k'一致。然而，我陷入了如何对这个频率进行排序的思考过程中，我所做的fc var是没用的。

At first I tried having another variable 'fc' (for frequency counter) to coincide with my original counter variable 'k'. However I am stuck in the thought process of how to go about sorting this frequency, the fc var I made is just useless.

感谢您提供的任何帮助！

Thanks for any help provided!

这是我的代码：

  import java.io.*;
public class Freq
{
    public static void main(String args[])throws IOException
    {
        //read input stream
        BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
        int ci,i,j,k,l,fc;l=0;
        String str,str1;
        char c,ch;
        System.out.println("Enter your String");
        str=in.readLine();
        i=str.length();
        //cycle through ASCII table chars and obtain chars typed
        for(c='A';c<='z';c++)
        {
            k=0;
            fc=0;           //fc keeps count like k
            for(j=0;j<i;j++)
            {
                ch=str.charAt(j);
                if(ch==c)
                    k++;
                    fc=k-1;     //was going to represent this counter for 'less than k'

            }
            if(k>0)
            System.out.println("The character "+c+" has occured for "+k+" times");
        }
    }
}

推荐答案

您需要先存储它们。您可以使用HashMap将它们全部存储起来，它还可以简化您的计数程序。然后在条目集上的Collections.sort。您需要制作一个Comparable>来比较排序的条目值。

You will need to store them all first. You can use a HashMap to store them all, it will also simplify your counting routine. Then Collections.sort on the entry set. You will need to make a Comparable> to compare the entry values for sorting.

编辑添加示例代码....

Edited to add sample code....

    BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
    System.out.println("Enter your String");
    String line = in.readLine();
    HashMap<Character,Integer> counts = new HashMap<>();
    for(char c : line.toCharArray()) {
        Integer count = counts.get(c);
        if (count == null) {
            count = 0;
        }
        counts.put(c, ++count);
    }
    List<Entry<Character,Integer>> list = new ArrayList<>(counts.entrySet());
    Collections.sort(list, new Comparator<Entry<Character,Integer>>() {
        @Override
        public int compare(Entry<Character, Integer> o1,
                Entry<Character, Integer> o2) {
            return o2.getValue() - o1.getValue();
        }
    });
    for(Entry<Character,Integer> entry : list) {
        System.out.println("The character "+entry.getKey() +" has occured for "+ entry.getValue()+" times");
    }

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