爪哇 - 如何找到一个HashMap是最接近于一个特定的数字的值？ [英] Java - How to find a value from a hashmap that is the closest to a particular number?

问题描述

您好我有一个的HashMap＆LT;弦乐，双＆GT; ，并返回称为答案双重值的函数。我想检查哪些HashMap中值是最接近的答案，然后抓住该值的键，并打印出来。

Hi I have a HashMap<String, Double> and also a function which returns a double value known as answer. I want to check which value in the HashMap is the closest to the answer and then grab that value's key and print it.

HashMap<String, Double> output = new HashMap<String, Double>();


contents
("A", 0)
("B", 0.25)
("C", 0.5)
("D", 0.75)
("E", 1)

假设的答案，我的职能之一是0.42，我怎么能检查哪些看重它最接近然后抓住关键的价值。我不能围绕HashMap中的键和值开关（为previous功能同样分配值，每个字母），否则倒不如去通过每一个键，得到的值。

Suppose the answer to one of my functions was 0.42, how can I check which value it is closest to and then grab the key to that value. I cant switch around the key and value of the HashMap (as a previous function assigns the values equally to each letter), otherwise it would be better to go through each key and get the value.

推荐答案

如果您的值是唯一的，你可以使用的 TreeMap的，它实现的NavigableMap ，它有漂亮的 ceilingKey 和 floorKey 方法：

If your values are unique, you can use a TreeMap, which implements NavigableMap, which has the nice ceilingKey and floorKey methods:

    NavigableMap<Double, String> map = new TreeMap<>();
    map.put(0d, "A");
    map.put(0.25, "B");
    map.put(0.5, "C");
    map.put(0.75, "D");
    map.put(1d, "E");

    double value = 0.42;
    double above = map.ceilingKey(value);
    double below = map.floorKey(value);

    System.out.println(value - below > above - value ? above : below); //prints 0.5

请注意：这两种方法可以返回null如果值小于最小/最大键

Note: both methods can return null if value is less (resp. greater) than the smallest / largest key.

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