Question

我想按照其值对树形图进行排序，我使用一组＆gt;要做到这一点，这是我的代码：

StringBuilder sb = new StringBuilder();
        Map<Character, Integer> map = new TreeMap<>();
        for (char c : s.toCharArray()){
            map.put(c, map.getOrDefault(c, 0) + 1);
        }
        TreeSet<Map.Entry<Character, Integer>> set = new TreeSet<Map.Entry<Character, Integer>>(){
            public int compare(Map.Entry<Character, Integer> e1, Map.Entry<Character, Integer> e2){
                return e2.getValue() - e1.getValue();
            }
        };
        for (Map.Entry<Character, Integer> e : map.entrySet()){
            set.add(e);
        }
        // set.addAll(map.entrySet());
        for (Map.Entry<Character, Integer> e : set){
            for (int i = 0; i < e.getValue(); i++){
                sb.append(e.getKey());
            }
        }
        return sb.toString();

但是我收到以下错误：

Exception in thread "main" java.lang.ClassCastException: java.util.TreeMap$Entry cannot be cast to java.lang.Comparable
    at java.util.TreeMap.compare(TreeMap.java:1251)
    at java.util.TreeMap.put(TreeMap.java:495)
    at java.util.TreeSet.add(TreeSet.java:212)
    at Solution.frequencySort(Solution.java:14)
    at __DriverSolution__.__helper__(__Driver__.java:4)
    at __Driver__.main(__Driver__.java:48)

那为什么我不能将entrySet添加到treeSet？

谢谢！

Answer 1

因为Map.Entry未实现Comparable。您还没有为Comparator提供TreeSet，即使您可能认为自己已经是var set = new TreeSet<>(Comparator.<Map.Entry<Character, Integer>, Integer>comparing(Map.Entry::getValue).reversed());。

使用Java 10，您可以使用以下内容：

number = input("Enter a whole number in the range of 1-99: ")
for i in range(int(number), 100, int(number)):
    print(i, end = ", ")

TreeMap按值错误排序

1 个答案: