Merge pull request blakeembrey#128 from roitt/longest-compound-word

Longest compound word using suffix trees.

Author: blakeembrey

solutions/java/LongestCompoundWord.java

@@ -0,0 +1,62 @@
+import java.util.ArrayList;
+import java.util.HashMap;
+
+public class LongestCompoundWord {
+	HashMap<String, String> suffixTree = new HashMap<String, String>();
+	ArrayList<String[]> queue = new ArrayList<String[]>();
+
+	public static void main(String[] args) {
+		LongestCompoundWord lcw = new LongestCompoundWord();
+		String[] input = { "cat", "cats", "catsdogcats", "catxdogcatsrat",
+				"dog", "dogcatsdog", "hippopotamuses", "rat", "ratcat",
+				"ratcatdog", "ratcatdogcat" };
+		System.out.println(lcw.getWord(input));
+	}
+
+	public String getWord(String[] input) {
+		String LongestWord = "";
+		// First round
+		for (int i = 0; i < input.length; i++) {
+			ArrayList<String[]> suffixes = getSuffixesForPrefixes(input[i],
+					input[i]);
+			if (suffixes.size() > 0) {
+				// Add the pair of original word and suffix to the queue
+				queue.addAll(suffixes);
+			}
+			suffixTree.put(input[i], input[i]);
+		}
+
+		// Empty the queue while searching for longest word
+		while (!queue.isEmpty()) {
+			String[] probePair = queue.get(0);
+			// Find possible valid and compound words
+			if (suffixTree.containsKey(probePair[1])) { // Valid word
+				if (probePair[0].length() > LongestWord.length())
+					LongestWord = probePair[0];
+			} else {
+				ArrayList<String[]> suffixes = getSuffixesForPrefixes(
+						probePair[0], probePair[1]);
+				if (suffixes.size() > 0) {
+					// Add the pair of original word and suffix to the queue
+					queue.addAll(suffixes);
+				}
+			}
+			queue.remove(0);
+		}
+		return LongestWord;
+	}
+
+	public ArrayList<String[]> getSuffixesForPrefixes(String originalWord,
+			String word) {
+		ArrayList<String[]> suffixes = new ArrayList<String[]>();
+		for (int i = 1; i <= word.length(); i++) {
+			if (suffixTree.containsKey(word.substring(0, i))) {
+				String[] pair = new String[2];
+				pair[0] = originalWord;
+				pair[1] = word.substring(i);
+				suffixes.add(pair);
+			}
+		}
+		return suffixes;
+	}
+}