【发布时间】：2015-08-24 18:55:39
【问题描述】：
我正在使用 Tries 数据结构根据号码前缀确定电话号码所属的国家/地区。
我正在使用 Vladimir Kroz 创建的 Tries 实现，效果非常好：here
这就是我填充 Tries 地图的方式：
private static Trie<Country> trie = new Trie<>();
trie.put("7", new Country(countryID, country));
trie.put("794", new Country(countryID, country));
如您所见，Tries 将电话号码前缀作为键，将 Country 对象作为值。
这就是我执行搜索的方式：
Country country = trie.get("79519637944");
String CountryName = country.getName();
如您所见，我使用电话号码作为关键字。现在 Tries 正在尝试为该号码查找匹配的前缀。尝试将从第一个数字开始尽可能地爬行。如果它在树中找不到任何匹配的数字，那么它将返回该特定前缀的值。
效果很好，但需要稍作调整。
假设我有前缀 7 和前缀 746。
现在，当我尝试查找电话号码 74568706987069 时，Tries 将返回 null，因为它会像这样爬入树中 7-> 4-> 将尝试找到 5，但它不会，因此它会返回值为与前缀 74 而不是 7 关联。
如何让它记住最后一个值不为空的前缀。
尝试代码如下（搜索发生在_get方法中）：
import java.util.HashMap;
import java.util.Map;
/**
* Prefix table based on trie structure. Allows to perform incremental lookup
* and match based on search key prefixes (classic example - determine phone
* area code for given phone number)
*
* @param <V>
* a type of value object to be stored along with prefix (e.g when
* key is a country name, the value could be a name of the country)
*
* @author Vladimir Kroz
*/
public class Trie<V> {
Entry<V> entry;
char key;
Map<Character, Trie<V>> childrens;
public Trie() {
this.childrens = new HashMap<Character, Trie<V>>(10);
entry = new Entry<V>();
}
/** non-public, used by _put() */
Trie(char key) {
this.childrens = new HashMap<Character, Trie<V>>(10);
this.key = key;
entry = new Entry<V>();
}
public void put(String key, V value) {
_put(new StringBuffer(key), new StringBuffer(""), value);
}
void _put(StringBuffer remainder, StringBuffer prefix, V value) {
if (remainder.length() > 0) {
char keyElement = remainder.charAt(0);
Trie<V> t = null;
try {
t = childrens.get(keyElement);
} catch (IndexOutOfBoundsException e) {
}
if (t == null) {
t = new Trie<V>(keyElement);
childrens.put(keyElement, t);
}
prefix.append(remainder.charAt(0));
t._put(remainder.deleteCharAt(0), prefix, value);
} else {
this.entry.value = value;
this.entry.prefix = prefix.toString();
}
}
/**
* Retrieves element from prefix table matching as a prefix to provided key.
* E.g. is key is "abcde" and prefix table has node "ab" then this call will
* return "ab"
*
* @param key
* a string which starts with prefix to be searched in the table
* (e.g. phone number)
* @return an Object assosiated with matching prefix (i.e if key is a phone
* number it may return a corresponding country name)
*/
public V get(String key) {
return _get(new StringBuffer(key), 0);
}
/**
* Returns true if key has matching prefix in the table
*/
public boolean hasPrefix(String key) {
return ((this.get(key) != null) ? true : false);
}
V _get(StringBuffer key, int level) {
if (key.length() > 0) {
Trie<V> t = childrens.get(key.charAt(0));
if (t != null) {
return t._get(key.deleteCharAt(0), ++level);
} else {
return (level > 0) ? entry.value : null;
}
} else {
return entry.value;
}
}
@Override
public String toString() {
return "Trie [entry=" + entry + ", key=" + key + ", childrens="
+ childrens + "]";
}
static public class Entry<V> {
String prefix;
V value;
public Entry() {
}
public Entry(String p, V v) {
prefix = p;
value = v;
}
public String prefix() {
return prefix;
}
public V value() {
return value;
}
@Override
public String toString() {
return "Entry [prefix=" + prefix + ", value=" + value + "]";
}
}
}
感谢任何帮助！
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