208 Implement Trie (Prefix Tree)¶

Leetcode

A trie (pronounced as "try") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.

Implement the Trie class:

Trie() Initializes the trie object.
void insert(String word) Inserts the string word into the trie.
boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.
boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.

Example 1:

Input
["Trie", "insert", "search", "search", "startsWith", "insert", "search"][], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
Output
[null, null, true, false, true, null, true]

Explanation
Trie trie = new Trie();
trie.insert("apple");
trie.search("apple"); // return True
trie.search("app"); // return False
trie.startsWith("app"); // return True
trie.insert("app");
trie.search("app"); // return True

C# Solution¶

using System;
using System.Collections.Generic;
namespace Algorithms.Medium
{
  public class TrieNode
  {
    public Dictionary<char, TrieNode> children;
    public bool endOfWord;
    public TrieNode()
    {
      children = new Dictionary<char, TrieNode>();
      endOfWord = false;
    }

  }
  public class Trie
  {
    public TrieNode root { get; private set; }
    public Trie()
    {
      root = new TrieNode();
    }

    public void Insert(string v)
    {
      var current = root;

      for (var i = 0; i < v.Length; i++)
      {
        if (!current.children.ContainsKey(v[i]))
        {
          current.children.Add(v[i], new TrieNode());
        }
        current = current.children[v[i]];
      }

      current.endOfWord = true;
    }

    public virtual bool Search(string v, bool isStartsWith = false)
    {
      var current = root;
      for (var i = 0; i < v.Length; i++)
      {
        if (!current.children.ContainsKey(v[i])) return false;

        current = current.children[v[i]];
      }

      return isStartsWith ? true : current.endOfWord;
    }

    public bool StartsWith(string v)
    {
      return Search(v, true);
    }
  }
}

C# Tests¶

using Algorithms.Medium;
using Xunit;

namespace AlgorithmTests.Medium
{
  public class TrieNodeTests
  {
    [Fact]
    public void TestTrie()
    {
      Trie trie = new Trie();
      trie.Insert("apple");

      Assert.True(trie.Search("apple"));
      Assert.False(trie.Search("app"));
      Assert.True(trie.StartsWith("app"));

      trie.Insert("app");
      Assert.True(trie.Search("app"));
    }
  }
}