208. Implement Trie (Prefix Tree)

Description

Implement a trie with insert, search, and startsWith methods.

Note:

• You may assume that all inputs are consist of lowercase letters a-z.

• All inputs are guaranteed to be non-empty strings.

Constraints

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

Example 1

Input:

["Trie", "insert", "search", "search", "startsWith", "insert", "search"]

[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]

Output:

[null, null, true, false, true, null, true]

Example 2

Solutions

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

class Trie {
    
    class TrieNode {
        TrieNode[] children;
        boolean isEnd;
        
        TrieNode() {
            children = new TrieNode[26];
        }
    }
    
    private TrieNode root;

    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode node = root;
        for(int i = 0; i < word.length(); i++) {
            int index = word.charAt(i)-'a';
            if(node.children[index] == null) {
                node.children[index] = new TrieNode();
            }
            node = node.children[index];
        }
        node.isEnd = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode node = searchPrefix(word);
        return node != null && node.isEnd;
    }
    
    /** Returns if there is any word in the trie that 
        starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode node = searchPrefix(prefix);
        return node != null;
    }
    
    private TrieNode searchPrefix(String word) {
        TrieNode node = root;
        for(int i = 0; i < word.length(); i++) {
            int index = word.charAt(i)-'a';
            if(node.children[index] == null) {
                return null;
            }
            node = node.children[index];
        }
        return node;
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */

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