从Java中的Map中获取值的范围

Question

是否有可能获得与Java Map中的一系列键匹配的值。 假设我有，

Map<Key,Value> //size 10,000
Key   - 9.0, 9.1, 9.5, 4.2, 4.3, 6.1, 6.6
Value - 10 , 20 , 30 , 40 , 20 , 60 , 10  

ArrayList alMatch = {1.0,4.0,6.0}

在这种情况下，对于值4.0，我想得到40（关键4.2）和20（关键4.3）。 所以我希望将所有值映射到Map中的键5.0 >= key>=4.0 。 是否可以通过Map或类似的数据结构来实现。

地图的大小很大。 或者是否有其他更好的方法以最小的复杂性实现相同的目标。

Answer 1

您可以使用NavigableMap的实现（示例TreeMap）。 这种方法特别值得您关注：

/**
 * Returns a view of the portion of this map whose keys range from
 * {@code fromKey} to {@code toKey}.  If {@code fromKey} and
 * {@code toKey} are equal, the returned map is empty unless
 * {@code fromExclusive} and {@code toExclusive} are both true.  The
 * returned map is backed by this map, so changes in the returned map are
 * reflected in this map, and vice-versa.  The returned map supports all
 * optional map operations that this map supports.
 *
 * <p>The returned map will throw an {@code IllegalArgumentException}
 * on an attempt to insert a key outside of its range, or to construct a
 * submap either of whose endpoints lie outside its range.
 *
 * @param fromKey low endpoint of the keys in the returned map
 * @param fromInclusive {@code true} if the low endpoint
 *        is to be included in the returned view
 * @param toKey high endpoint of the keys in the returned map
 * @param toInclusive {@code true} if the high endpoint
 *        is to be included in the returned view
 * @return a view of the portion of this map whose keys range from
 *         {@code fromKey} to {@code toKey}
 * @throws ClassCastException if {@code fromKey} and {@code toKey}
 *         cannot be compared to one another using this map's comparator
 *         (or, if the map has no comparator, using natural ordering).
 *         Implementations may, but are not required to, throw this
 *         exception if {@code fromKey} or {@code toKey}
 *         cannot be compared to keys currently in the map.
 * @throws NullPointerException if {@code fromKey} or {@code toKey}
 *         is null and this map does not permit null keys
 * @throws IllegalArgumentException if {@code fromKey} is greater than
 *         {@code toKey}; or if this map itself has a restricted
 *         range, and {@code fromKey} or {@code toKey} lies
 *         outside the bounds of the range
 */
NavigableMap<K,V> subMap(K fromKey, boolean fromInclusive,
                         K toKey,   boolean toInclusive);

TreeMap的底层数据结构是红色和黑色树，所有复杂性都由NavigableMap接口抽象，因此使用起来非常简单。