Java - 如何从最接近特定数字的哈希图中找到一个值?
您好，我有一个 HashMap<String, Double> 以及一个返回双精度值的函数，称为 answer.我想检查 HashMap 中的哪个值最接近答案，然后获取该值的键并打印它.
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)
假设我的一个函数的答案是 0.42，我如何检查它最接近哪个值，然后获取该值的键.我无法切换 HashMap 的键和值(因为之前的函数将值平均分配给每个字母)，否则最好遍历每个键并获取值.
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
如果你的值是唯一的，你可以使用 TreeMap，实现 NavigableMap，它有很好的 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
注意:如果 value 小于(或大于)最小/最大键，则两种方法都可以返回 null.
Note: both methods can return null if value is less (resp. greater) than the smallest / largest key.
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