treemap | 易学教程

Java data structure that acts like TreeMap + Hash?

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问题 I need to enter key-value pairs into a data structure that allows me to retrieve them in ascending order of the key--BUT their may be many keys of the same value. Thus, if the kv-pairs were {10-a, 10-b, 9-c, 8-d, 8-e, 8-f, 4-g, 4-h, 2-i} I would need to retrieve the values in the order: a, b ,c, d, e, f, g, h, i. Are there any data structures in the JAVA API that supports this? I tried using a TreeMap because it kept them in order which allowed me to use TreeMap.lastKey() to retrieve the

Time complexity of TreeMap<> operations: get() and subMap()

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问题 Based on this post, Time complexity of TreeMap operations- subMap, headMap, tailMap subMap() itself is O(1), and O(n) comes from iterating the sub map. So, why use get(key) then? We can use subMap(key, true, key, true) instead, which is O(1) and iterating this sub map is also O(1). Faster than get(key), which is O(log(n)). Something wrong here... 回答1: We can use subMap(key, true, key, true) instead, which is O(1) This is correct and iterating this sub map is also O(1). O(n) comes from the

Failed test case, what am I doing wrong?

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问题 I've been trying to get this to work, but I'm not quite sure where I'm going wrong. It'll make sense with the test case in a bit. Some things about what I'm doing. The list must have one or more lines. If there's not at least one line, an IllegalArgumentException is thrown. Each line has some kind of String, then a tab character, then a double, then a newline. If any lines don't follow this pattern, then an IllegalArgumentException would also be thrown. This is ideally supposed to work if you

Treemap visualisation with PHP?

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问题 There seem to be examples for TreeMaps for almost every language but PHP. Has anyone got a link to some basic code? 回答1: http://www.neurofuzzy.net/2006/04/28/treemap-php-source-code/ http://powernerd.blogspot.com/2007/06/treemaps-with-php.html 来源： https://stackoverflow.com/questions/2139137/treemap-visualisation-with-php

Java集合容器系列05-TreeMap

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一、TreeMap的介绍 TreeMap继承自AbstractMap，实现了NavigableMap，基于红黑树实现，它内部的键值对映射是按照类内部指定的比较器Comparator进行排序，如果内部的排序器为空则根据键值对映射中Key的自然顺序进行排序，取决于实例化对象时使用的构造函数。Treemap的底层红黑树结构保证了containKey、get、put、remove方法定位Key操作的时间复杂度为O(logN)。TreeMap是非线程安全的，在创建容器迭代器Iterator之后如果有其他线程对容器做出结构性修改（添加、插入、删除键值对均属于结构性修改，修改已存在键值对的value值不算结构性修改）会抛出一个ConcurrentModificationException异常。二、TreeMap的数据结构 1 - 继承结构 public class TreeMap<K,V> extends AbstractMap<K,V> implements NavigableMap<K,V>, Cloneable, java.io.Serializable 从源码中可以看出TreeMap继承AbstractMap，AbstractMap实现了Map的一些基本操作，此外是实现了NavigableMap、Cloneable、java.io.Serializable接口

Make TreeMap Comparator tolerate null

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问题 This customized Valuecomparator sorts the TreeMap by it's value. But it doesn't tolerate nullpointexception when searching whether the TreeMap has a certain key. How do i modify the comparator to handle the nullpoint? import java.io.IOException; import java.util.Comparator; import java.util.HashMap; import java.util.Map; import java.util.TreeMap; public class TestTreeMap { public static class ValueComparator<T> implements Comparator<Object> { Map<T, Double> base; public ValueComparator(Map<T,

Is it possible to create a Map that has ArrayList properties with log(n) complexity?

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问题 I am trying to build a generic data structure that needs to hold keys and values and in the same time keep track on the index's in which key's and values were put in like arraylist do just in a complexity of O(log n) or less. I tryed to work around a solution to this problem and created various TreeMaps that has Integer - index's and valuse and vise-versa, and the same with keys. Just to make it more clear, the Index's symbolize the insertion order from the user. so if I had 3 elements then

Comparator<String> must override super class method

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问题 I'm making a TreeMap<String, String> and want to order it in a descending fashion. I created the following comparator: Comparator<String> descender = new Comparator<String>() { @Override public int compare(String o1, String o2) { return o2.compareTo(o1); } }; I construct the TreeMap like so: myMap = new TreeMap<String, String>(descender); However, I'm getting the following error: The method compare(String, String) of type new Comparator<String>(){} must override a superclass method I've never

好程序员Java教程分享Java实习生面试题集锦

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　　今天好程序员小编总结了一些关于Java的面试题，希望能帮助到正在求职的你! 　　1、Java的数据结构你用过那些?map与set的本质区别是什么　　数据结构：是指相互之间存在一种或多种特定关系的数据元素的集合。　　依据逻辑关系，数据结构分为：线性和非线性数据结构。　　2、Map与Set的本质区别是什么? 　　Set不能包含重复的元素，zui多有一个空值，继承自Collection接口，底层是Map实现机制。Map不能包含重复的键，每个键zui多对应一个映射的值，不能有空值键。两接口提供的方法不完全一样。　　3、Java常见的数据结构有哪些? 　　Java常见的数据结构有Collection和Map，其中Collection接口下包括List和Set接口，其下又有多个实现类如List下有ArrayList、LinkedList和Vector等实现类，Set下有HashSet、LinkedSet等实现类和SortedSet接口，HashSet下有LinkedHashSet子类，SortedSet接口下有TreeSet实现类。Map接口下有HashMap(有LinkedHashMap子类)、HashTable(有Properties子类)实现类和SortedMap接口(有TreeMap实现类)。　　Java的数据结构主要有List、Set、Map、ArrayList

TreeMap<String, Integer> object's get method return null value

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import java.util.*; public class Sort { static class ValueComparator implements Comparator<String> { Map<String, Integer> base; ValueComparator(Map<String, Integer> base) { this.base = base; } @Override public int compare(String a, String b) { if (base.get(a) >= base.get(b)) { return 1; } else { return -1; } } } public static void main(String[] args) { HashMap<String, Integer> map = new HashMap<String, Integer>(); ValueComparator vc = new ValueComparator(map); TreeMap<String, Integer> sorted = new TreeMap<String, Integer>(vc); map.put("A", 1); map.put("B", 2); sorted.putAll(map); for (String