小编典典

树状图 删除不起作用

java

我试图通过执行以下循环来获取TreeMap的前10个元素:

        TreeMap<Integer, Integer> sortedMap = sortMap(m);
        String outString = "";
        int count = 10;
        while (count > 0) {
            count--;
            Integer k = sortedMap.firstKey();
            outString += String.valueOf(k);
            sortedMap.remove(k);
            if (count != 0) {
                outString += ",";
            }
        }

        System.out.println("outVal is " + outVal);

该打印outVal is 11377,11377,11377,11377,11377,11377,11377,11377,11377,11377
Integer工具Comparable,为什么可能remove不起作用?

更新 这是我的sortMap实现:

        public static TreeMap<Integer, Integer> sortMap(HashMap<Integer, Integer> map) {
           ValueComparator bvc =  new ValueComparator(map);
           TreeMap<Integer,Integer> sorted_map = new TreeMap<Integer,Integer>(bvc);
           sorted_map.putAll(map);
           return sorted_map;
        }

class ValueComparator implements Comparator<Integer> {
    java.util.Map<Integer, Integer> base;
    public ValueComparator(java.util.Map<Integer, Integer> base) {
        this.base = base;
    }

    // Note: this comparator imposes orderings that are inconsistent with equals.    
    public int compare(Integer a, Integer b) {
        if (base.get(a) >= base.get(b)) {
            return -1;
        } else {
            return 1;
        } // returning 0 would merge keys
    }
}

更新 这很有用:Java Map按值排序


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2020-10-16

共1个答案

小编典典

public int compare(Integer a, Integer b) {
if (base.get(a) >= base.get(b)) {
return -1;
} else {
return 1;
} // returning 0 would merge keys
}

此比较器有缺陷,因为(除与之不一致之外equals)它不满足表示compare(a,b) > 0暗示的比较器协定,compare(b,a) < 0反之亦然。而且由于TreeMap依赖于比较器返回0来查找您要尝试找到的密钥,remove()所以它将永远无法删除任何内容-
无论您尝试使用哪种密钥并搜索映射,都永远不会认为该密钥存在。

2020-10-16

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