Question
Write an autocomplete class that returns all dictionary words with a given prefix.
eg.
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dict: {"abc", "acd", "bcd", "def", "a", "aba"} prefix: "a" -> "abc", "acd", "a", "aba" prefix: "b" -> "bcd" |
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Solution
How was that problem? You can check out the solution in the video below.
Here is the source code for the solution shown in the video (Github):
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// Trie node class private class Node { String prefix; HashMap<Character, Node> children; // Does this node represent the last character in a word? boolean isWord; private Node(String prefix) { this.prefix = prefix; this.children = new HashMap<Character, Node>(); } } // The trie private Node trie; // Construct the trie from the dictionary public Autocomplete(String[] dict) { trie = new Node(""); for (String s : dict) insertWord(s); } // Insert a word into the trie private void insertWord(String s) { // Iterate through each character in the string. If the character is not // already in the trie then add it Node curr = trie; for (int i = 0; i < s.length(); i++) { if (!curr.children.containsKey(s.charAt(i))) { curr.children.put(s.charAt(i), new Node(s.substring(0, i + 1))); } curr = curr.children.get(s.charAt(i)); if (i == s.length() - 1) curr.isWord = true; } } // Find all words in trie that start with prefix public List<String> getWordsForPrefix(String pre) { List<String> results = new LinkedList<String>(); // Iterate to the end of the prefix Node curr = trie; for (char c : pre.toCharArray()) { if (curr.children.containsKey(c)) { curr = curr.children.get(c); } else { return results; } } // At the end of the prefix, find all child words findAllChildWords(curr, results); return results; } // Recursively find every child word private void findAllChildWords(Node n, List<String> results) { if (n.isWord) results.add(n.prefix); for (Character c : n.children.keySet()) { findAllChildWords(n.children.get(c), results); } } |
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