1 /* 2 * Copyright (c) 2013 Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 24 package org.openjdk.bench.java.util.stream.tasks.PhoneCode; 25 26 import org.openjdk.bench.java.util.stream.tasks.DataProviders; 27 28 import java.util.Arrays; 29 import java.util.Collection; 30 import java.util.Collections; 31 import java.util.HashMap; 32 import java.util.List; 33 import java.util.Map; 34 import java.util.concurrent.ConcurrentHashMap; 35 import java.util.stream.Collectors; 36 import java.util.stream.Stream; 37 38 /** 39 * The phone coder problem is trying to find full list of possible 40 * mnemonic combination of numbers. 41 * 42 * The solution is based on Martin Odersky's devoxx 2010 scala talk, 43 * where numbers are not allowed in the result, which is not really 44 * correct, but we don't care. 45 */ 46 public class PhoneCodeProblem { 47 // Map Character 'A'-'Z' to digits "2"-"9", key is charCode 48 private static final Map<Integer, String> CHAR_CODE; 49 // Map a string of digits to a collection of dictionary words 50 private static final Map<String, List<String>> WORD_CODES; 51 52 static { 53 HashMap<String, String> mnemonics = new HashMap<>(8); 54 mnemonics.put("2", "ABC"); 55 mnemonics.put("3", "DEF"); 56 mnemonics.put("4", "GHI"); 57 mnemonics.put("5", "JKL"); 58 mnemonics.put("6", "MNO"); 59 mnemonics.put("7", "PQRS"); 60 mnemonics.put("8", "TUV"); 61 mnemonics.put("9", "WXYZ"); 62 63 CHAR_CODE = new ConcurrentHashMap<>(); 64 mnemonics.entrySet().stream().forEach(e -> 65 e.getValue().chars().forEach(c -> 66 { CHAR_CODE.put(c, e.getKey()); } )); 67 68 WORD_CODES = loadDictionary(); 69 // System.out.println("Dictionary loaded with " + WORD_CODES.size() + " number entries"); 70 } 71 72 // Convert a word to its number form wordToNumber(String word)73 private static String wordToNumber(String word) { 74 return word.chars().mapToObj(CHAR_CODE::get) 75 .reduce("", String::concat); 76 } 77 78 // Prepare number -> word lookup table loadDictionary()79 private static Map<String, List<String>> loadDictionary() { 80 try (Stream<String> s = DataProviders.dictionary()) { 81 return s.filter(w -> w.length() > 1) 82 .filter(w -> w.matches("[a-zA-Z]*")) 83 .map(String::toUpperCase) 84 .collect(Collectors.groupingBy(PhoneCodeProblem::wordToNumber)); 85 } catch (Exception ex) { 86 ex.printStackTrace(System.err); 87 return Collections.emptyMap(); 88 } 89 } 90 wordsForNumber(String number)91 public static Collection<String> wordsForNumber(String number) { 92 Collection<String> rv = WORD_CODES.get(number); 93 return (null == rv) ? Collections.emptySet() : rv; 94 } 95 get(int length)96 public static Stream<String> get(int length) { 97 String digits[] = { "2", "3", "4", "5", "6", "7", "8", "9" }; 98 99 Stream<String> s = Arrays.stream(digits); 100 for (int i = 1; i < length; i++) { 101 s = s.flatMap(d1 -> Arrays.stream(digits).map(d2 -> d1 + d2)); 102 } 103 return s; 104 } 105 } 106