Solves string decompression problem with parser combinators
This commit is contained in:
parent
6048270224
commit
21edb50158
4
pom.xml
4
pom.xml
@ -13,8 +13,8 @@
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-compiler-plugin</artifactId>
|
||||
<configuration>
|
||||
<source>8</source>
|
||||
<target>8</target>
|
||||
<source>9</source>
|
||||
<target>9</target>
|
||||
</configuration>
|
||||
</plugin>
|
||||
</plugins>
|
||||
|
233
src/main/java/net/abhinavsarkar/former/StringDecompression.java
Normal file
233
src/main/java/net/abhinavsarkar/former/StringDecompression.java
Normal file
@ -0,0 +1,233 @@
|
||||
package net.abhinavsarkar.former;
|
||||
|
||||
import java.util.ArrayList;
|
||||
import java.util.List;
|
||||
import java.util.Optional;
|
||||
import java.util.function.BiFunction;
|
||||
import java.util.function.Function;
|
||||
import java.util.function.Predicate;
|
||||
import java.util.stream.Collectors;
|
||||
import java.util.stream.Stream;
|
||||
|
||||
/**
|
||||
* https://techdevguide.withgoogle.com/resources/compress-decompression/
|
||||
*/
|
||||
public class StringDecompression {
|
||||
public static void main(String[] args) {
|
||||
System.out.println(decompress("10[a]"));
|
||||
System.out.println(decompress("3[abc]4[ab]c"));
|
||||
System.out.println(decompress("2[3[a]b]"));
|
||||
System.out.println(decompress("2[]b"));
|
||||
System.out.println(decompress("0[abc]v"));
|
||||
System.out.println(decompress("szs"));
|
||||
}
|
||||
|
||||
static String decompress(String s) {
|
||||
return parse(s).toString();
|
||||
}
|
||||
|
||||
private static CompressedString parse(String s) {
|
||||
Optional<Tuple<String, CompressedString>> parsed = CompressedString.PARSER.parse(s);
|
||||
if (!parsed.isPresent()) {
|
||||
throw new IllegalArgumentException("Unable to decompress");
|
||||
}
|
||||
return parsed.get().second;
|
||||
}
|
||||
}
|
||||
|
||||
class Tuple<A, B> {
|
||||
A first;
|
||||
B second;
|
||||
|
||||
Tuple(A first, B second) {
|
||||
this.first = first;
|
||||
this.second = second;
|
||||
}
|
||||
|
||||
<C> Tuple<A, C> map(Function<B, C> f) {
|
||||
return new Tuple<>(first, f.apply(second));
|
||||
}
|
||||
}
|
||||
|
||||
@FunctionalInterface
|
||||
interface Parser<I, O> {
|
||||
Optional<Tuple<I, O>> parse(I input);
|
||||
|
||||
default <P> Parser<I, P> map(Function<O, P> mapper) {
|
||||
return input -> this.parse(input).map(tup -> tup.map(mapper));
|
||||
}
|
||||
|
||||
default <P> Parser<I, P> seqApply(Parser<I, Function<O, P>> parser) {
|
||||
return input -> parser.parse(input)
|
||||
.flatMap(ftup -> this.parse(ftup.first).map(tup -> tup.map(ftup.second)));
|
||||
}
|
||||
|
||||
default <P> Parser<I, P> leftSeqApply(Parser<I, P> parser) {
|
||||
return this.apply((x, y) -> y, parser);
|
||||
}
|
||||
|
||||
default <P> Parser<I, O> rightSeqApply(Parser<I, P> parser) {
|
||||
return this.apply((x, y) -> x, parser);
|
||||
}
|
||||
|
||||
default <P, Q> Parser<I, Q> apply(BiFunction<O, P, Q> function, Parser<I, P> parser) {
|
||||
return parser.seqApply(this.map(o -> p -> function.apply(o, p)));
|
||||
}
|
||||
|
||||
default Parser<I, O> or(Parser<I, O> parser) {
|
||||
return input -> this.parse(input).or(() -> parser.parse(input));
|
||||
}
|
||||
|
||||
default Parser<I, List<O>> many() {
|
||||
return input -> {
|
||||
I rest = input;
|
||||
List<O> output = new ArrayList<>();
|
||||
|
||||
Optional<Tuple<I, O>> parsed = this.parse(rest);
|
||||
while (parsed.isPresent()) {
|
||||
Tuple<I, O> tup = parsed.get();
|
||||
rest = tup.first;
|
||||
output.add(tup.second);
|
||||
parsed = this.parse(rest);
|
||||
}
|
||||
return Optional.of(new Tuple<>(rest, output));
|
||||
};
|
||||
}
|
||||
|
||||
default Parser<I, List<O>> some() {
|
||||
return input -> {
|
||||
Tuple<I, List<O>> output = many().parse(input).get();
|
||||
if (output.second.isEmpty()) {
|
||||
return Optional.empty();
|
||||
} else {
|
||||
return Optional.of(output);
|
||||
}
|
||||
};
|
||||
}
|
||||
|
||||
}
|
||||
|
||||
class CharPredicateParser implements Parser<String, Character> {
|
||||
private Predicate<Character> predicate;
|
||||
|
||||
CharPredicateParser(Predicate<Character> predicate) {
|
||||
this.predicate = predicate;
|
||||
}
|
||||
|
||||
@Override
|
||||
public Optional<Tuple<String, Character>> parse(String input) {
|
||||
if (input.isEmpty()) {
|
||||
return Optional.empty();
|
||||
}
|
||||
|
||||
Character i = input.charAt(0);
|
||||
if (predicate.test(i)) {
|
||||
return Optional.of(new Tuple<>(input.substring(1), i));
|
||||
}
|
||||
|
||||
return Optional.empty();
|
||||
}
|
||||
}
|
||||
|
||||
class Parsers {
|
||||
public static final Parser<String, Character> DIGIT_PARSER =
|
||||
new CharPredicateParser(Character::isDigit);
|
||||
|
||||
public static final Parser<String, Integer> NUMBER_PARSER =
|
||||
DIGIT_PARSER
|
||||
.some()
|
||||
.map(Parsers::digitsToInt);
|
||||
|
||||
public static final Parser<String, Character> ENGLISH_LOWER_CASE_CHAR_PARSER =
|
||||
new CharPredicateParser(c -> c >= 97 && c <= 122);
|
||||
|
||||
public static Parser<String, Character> charParser(Character c) {
|
||||
return new CharPredicateParser(c::equals);
|
||||
}
|
||||
|
||||
private static Integer digitsToInt(List<Character> digits) {
|
||||
int i = 0;
|
||||
for (char c : digits) {
|
||||
i = i * 10 + (c - 48);
|
||||
}
|
||||
return i;
|
||||
}
|
||||
}
|
||||
|
||||
class CompressedString {
|
||||
private List<Part> parts;
|
||||
|
||||
CompressedString(List<Part> parts) {
|
||||
this.parts = parts;
|
||||
}
|
||||
|
||||
interface Part {
|
||||
String toString();
|
||||
}
|
||||
|
||||
@Override
|
||||
public String toString() {
|
||||
return parts.stream()
|
||||
.map(Object::toString)
|
||||
.collect(Collectors.joining());
|
||||
}
|
||||
|
||||
public static final Parser<String, CompressedString> PARSER =
|
||||
CompressedPart.PARSER
|
||||
.or(StringPart.PARSER)
|
||||
.many()
|
||||
.map(CompressedString::new);
|
||||
}
|
||||
|
||||
|
||||
class StringPart implements CompressedString.Part {
|
||||
private String string;
|
||||
|
||||
StringPart(String string) {
|
||||
this.string = string;
|
||||
}
|
||||
|
||||
@Override
|
||||
public String toString() {
|
||||
return this.string;
|
||||
}
|
||||
|
||||
public static final Parser<String, CompressedString.Part> PARSER =
|
||||
Parsers.ENGLISH_LOWER_CASE_CHAR_PARSER
|
||||
.some()
|
||||
.map(chars -> new StringPart(charListToString(chars)));
|
||||
|
||||
private static String charListToString(List<Character> chars) {
|
||||
return chars.stream()
|
||||
.map(String::valueOf)
|
||||
.collect(Collectors.joining());
|
||||
}
|
||||
}
|
||||
|
||||
class CompressedPart implements CompressedString.Part {
|
||||
private int repetition;
|
||||
private CompressedString string;
|
||||
|
||||
CompressedPart(int repetition, CompressedString string) {
|
||||
this.repetition = repetition;
|
||||
this.string = string;
|
||||
}
|
||||
|
||||
@Override
|
||||
public String toString() {
|
||||
String s = string.toString();
|
||||
return Stream.generate(() -> s)
|
||||
.limit(repetition)
|
||||
.collect(Collectors.joining());
|
||||
}
|
||||
|
||||
private static final Parser<String, CompressedString> BRACKETED_STRING_PARSER =
|
||||
Parsers.charParser('[')
|
||||
.leftSeqApply(input -> CompressedString.PARSER
|
||||
.rightSeqApply(Parsers.charParser(']'))
|
||||
.parse(input));
|
||||
|
||||
public static final Parser<String, CompressedString.Part> PARSER =
|
||||
Parsers.NUMBER_PARSER.apply(CompressedPart::new, BRACKETED_STRING_PARSER);
|
||||
}
|
||||
|
Loading…
Reference in New Issue
Block a user