java将整数数组按频率降序排序

Question

我需要从jTextFrame中提取一个字符串，然后按出现的顺序排序，然后打印出来。babablackbike return:bbbbaakceil

    String word = (String)jTextField1.getText();
    String indexes = "abcdefghijklmnopqrstuvwxyz";
    int[] count = new int[indexes.length()];

    for (int i = 0; i < word.length(); i++) 
    {
        int index = indexes.indexOf(word.charAt(i));

        if (index < 0)
            continue;

        count[index]++;
    }

    for (int j = 0; j < count.length; j++) 
    {
        if (count[j] < 1)
            continue;

        char[] indiv = indexes.toCharArray();

        for (int p = 0; p < count[j];p++)
        {
            jTextArea1.append(""+indiv[j]);
            System.out.println(indiv[(j)] +"="+ count[j] + p);
        }     
    }

Answer 1

首先需要获得输入中每个字符的计数：

final String in = "babablackbike";
final Map<Character, Integer> counts = new HashMap<>();
final List<Character> inList = new ArrayList<>();
for (final char c : in.toCharArray()) {
    Integer count = counts.get(c);
    if (count == null) {
        counts.put(c, 1);
    } else {
        counts.put(c, count + 1);
    }
    inList.add(c);
}

由于Java在char[]与Character[]之间有点特殊——由于泛型不能处理原语，因此无法使用自定义比较器对原语进行排序——我同时也构建了一个List<Character>

现在我们只需要使用自定义Comparator和Map counts中的信息对List<Character>进行排序：

Collections.sort(inList, new Comparator<Character>() {

    @Override
    public int compare(final Character o1, final Character o2) {
        int c = counts.get(o1).compareTo(counts.get(o2));
        if (c != 0) {
            return -c;
        }
        return o1.compareTo(o2);
    }
});

因此，首先我们按照输入中字符的计数进行排序（逆序），然后我们按照字符本身进行排序

现在我们只需要将List构建回String：

final StringBuilder outBuilder = new StringBuilder();
for (final Character c : inList) {
    outBuilder.append(c);
}
System.out.println(outBuilder.toString());

输出：

bbbbaaakkceil

Answer 2

我认为，最好的解决方案是创建这样的HashMap

Map<Character, Integer> quantity = new HashMap<Character, Integer>();

然后，你可以这样做一个循环：

for (int i = 0; i < str.length() - 1; i++) {
  char c = str.charAt(i);
  // increment value of c in quantity map
}

之后，您可以按值对其进行排序并轻松打印

Answer 3

以下是一般算法：

1. 将字符串中的每个字符映射到它出现的次数
2. 按值（计数）的降序对地图键（字符）进行排序
3. 根据每个字符在字符串中出现的次数打印每个字符

---

下面是一个编码示例：

public void Print(String string)
{
    HashMap<Character,Integer> hashMap = new HashMap<Character,Integer>();
    TreeMap<Character,Integer> treeMap = new TreeMap<Character,Integer>(new ValueComparator(hashMap));
    for (Character key : string.toCharArray())
    {
        Integer value = hashMap.get(key);
        if (value == null)
            hashMap.put(key,1);
        else
            hashMap.put(key,value+1);
    }
    treeMap.putAll(hashMap);
    for (Character key : treeMap.keySet())
    {
        Integer value = hashMap.get(key);
        for (Integer i=0; i<value; i++)
            System.out.print(key);
    }
}

private class ValueComparator implements Comparator<Character>
{
    Map<Character,Integer> base;
    public ValueComparator(Map<Character,Integer> base)
    {
        this.base = base;
    }
    public int compare(Character a,Character b)
    {
        if (base.get(a) >= base.get(b))
            return -1;
        else
            return +1;
    }
}