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import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Queue;
public class Trie {
public static class TrieNode {
private TrieNode children[] = new TrieNode[26];
private boolean isWord = false;
private char character;
private TrieNode parent;
public TrieNode(){}
public TrieNode(char c, TrieNode parent) {
this.character = c;
this.parent = parent;
}
public TrieNode getChildren(char c) {
return children[(int)c - 97];
}
public ArrayList<TrieNode> getAllChildren() {
ArrayList<TrieNode> out = new ArrayList<>();
for (TrieNode child : children) {
if (child != null) {
out.add(child);
}
}
return out;
}
public TrieNode setChild(char c, TrieNode parent) {
children[(int)c - 97] = new TrieNode(c, parent);
return children[(int)c - 97];
}
public void setWord(boolean isWord) {
this.isWord = isWord;
}
public boolean isWord() {
return isWord;
}
public char getChar() {
return character;
}
public TrieNode getParent() {
return parent;
}
}
TrieNode root = new TrieNode();
public void add(String key) {
TrieNode temp = root;
for (char c : key.toLowerCase().toCharArray()) {
TrieNode next = temp.getChildren(c);
if (next == null) {
next = temp.setChild(c, temp);
}
temp = next;
}
temp.setWord(true);
}
public boolean contains(String str) {
TrieNode temp = root;
for (char c : str.toLowerCase().toCharArray()) {
TrieNode next = temp.getChildren(c);
if (next == null) {
return false;
}
temp = next;
}
return temp.isWord();
}
public ArrayList<String> getWords(String prefix) {
TrieNode temp = root;
ArrayList<String> words = new ArrayList<>();
for (char c : prefix.toLowerCase().toCharArray()) {
TrieNode next = temp.getChildren(c);
if (next == null) {
System.out.println("No words...");
return words;
}
temp = next;
}
TrieNode rel_root = temp;
Queue<TrieNode> q = new LinkedList<TrieNode>();
ArrayList<TrieNode> endingChars = new ArrayList<>();
q.add(rel_root);
while (q.isEmpty() == false) {
temp = q.remove();
if (temp.isWord()) {
endingChars.add(temp);
}
for (TrieNode child : temp.getAllChildren()) {
q.add(child);
}
}
// using a stack and a depth first algo would be better.
// instead we backtrack the parents until we get to the parent
for (TrieNode t : endingChars) {
temp = t;
String word = String.format("%c", t.getChar());
do {
temp = temp.getParent();
word = temp.getChar() + word;
} while (temp != rel_root);
words.add(prefix + word.substring(1));
}
return words;
}
public static void main(String[] args) {
Trie trie = new Trie();
String dict[] = {"cheers", "cheese", "chat", "bat"};
for (String w : dict) {
trie.add(w);
System.out.println(String.format("Added '%s' to trie...", w));
}
System.out.println("\nchips: " + trie.contains("chips"));
System.out.println("cheese: " + trie.contains("cheese"));
System.out.println("cat: " + trie.contains("cat"));
System.out.println("bat: " + trie.contains("bat"));
String prefixChecks[] = {"ch", "chee", "b"};
for (String prefix : prefixChecks) {
System.out.println("\nChecking prefixes for: '" + prefix + "':");
for (String word : trie.getWords(prefix)) {
System.out.println(word);
}
}
}
}
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