A minimal perfect hash function maps a set of string to an initial segment of the natural * numbers, but will actually map any string to that segment. We can check that * a string is part of the key set by hashing it to a value h, and checking that the h-th * string of the original list does coincide. Since, moreover, this class implements {@link StringMap}, * and thus {@linkplain #list() exposes the original list}, we have a two-way * dictionary. In other words, this is a full {@link StringMap} implementation. * *
Note that some care must be exercised: {@link CharSequence}'s contract does not * prescribe equality by content, so if your function behaves badly on some implementations of * {@link CharSequence} you might make the checks fail. To avoid difficulties, the * constructor checks that every string in the list is hashed correctly. * *
For the same reason, this class implements StringMap<MutableString>, and
* requires that the list of strings provided at construction time is actually a list of
* {@linkplain MutableString mutable strings}.
*
*
A typical usage of this class pairs a {@link FrontCodedStringList} with some kind
* of succinct structure from Sux4J.
*
* @author Sebastiano Vigna
* @since 1.0.8
*/
public class LiterallySignedStringMap extends AbstractObject2LongFunctionlist to its ordinal position.
* @param list a list of strings.
*/
public LiterallySignedStringMap(final Object2LongFunction function, final ObjectList list) {
this.function = function;
this.list = list;
size = list.size();
for(int i = 0; i < size; i++) if (function.getLong(list.get(i)) != i) throw new IllegalArgumentException("Function and list do not agree");
defRetValue = -1;
}
@SuppressWarnings("null")
@Override
public long getLong(final Object o) {
final CharSequence s = (CharSequence)o;
final long index = function.getLong(s);
return index >= 0 && index < size && list.get((int)index).equals(s) ? index : defRetValue;
}
@SuppressWarnings("null")
@Deprecated
@Override
public Long get(final Object o) {
final CharSequence s = (CharSequence)o;
final long index = function.getLong(s);
return index >= 0 && index < size && list.get((int)index).equals(s) ? Long.valueOf(index) : null;
}
@Override
public int size() {
return list.size();
}
@Override
public boolean containsKey(final Object o) {
return getLong(o) != -1;
}
@Override
public ObjectList list() {
return list;
}
@SuppressWarnings("unchecked")
public static void main(final String[] arg) throws IOException, JSAPException, ClassNotFoundException, SecurityException, NoSuchMethodException {
final SimpleJSAP jsap = new SimpleJSAP(LiterallySignedStringMap.class.getName(), "Builds a shift-add-xor signed string map by reading a newline-separated list of strings and a function built on the same list of strings.",
new Parameter[] {
new FlaggedOption("encoding", ForNameStringParser.getParser(Charset.class), "UTF-8", JSAP.NOT_REQUIRED, 'e', "encoding", "The string file encoding."),
new Switch("zipped", 'z', "zipped", "The string list is compressed in gzip format."),
new Switch("text", 't', "text", "The string list actually a text file, with one string per line."),
new UnflaggedOption("function", JSAP.STRING_PARSER, JSAP.NO_DEFAULT, JSAP.REQUIRED, JSAP.NOT_GREEDY, "The filename of the function to be signed."),
new UnflaggedOption("list", JSAP.STRING_PARSER, JSAP.NO_DEFAULT, JSAP.REQUIRED, JSAP.NOT_GREEDY, "The filename of the serialised list of strings, or of a text file containing a list of strings, if -t is specified."),
new UnflaggedOption("map", JSAP.STRING_PARSER, JSAP.NO_DEFAULT, JSAP.REQUIRED, JSAP.NOT_GREEDY, "The filename of the resulting map."),
});
final JSAPResult jsapResult = jsap.parse(arg);
if (jsap.messagePrinted()) return;
final String functionName = jsapResult.getString("function");
final String listName = jsapResult.getString("list");
final String mapName = jsapResult.getString("map");
final Charset encoding = (Charset)jsapResult.getObject("encoding");
final boolean zipped = jsapResult.getBoolean("zipped");
final boolean text = jsapResult.getBoolean("text");
final ObjectList