Counting the number of words in a Trie
Last Updated : 14 Feb, 2023
A Trie is used to store dictionary words so that they can be searched efficiently and prefix search can be done. The task is to write a function to count the number of words. Example :
Input : root / \ \ t a b | | | h n y | | \ | e s y e / | | i r w | | | r e e | r Output : 8 Explanation : Words formed in the Trie : "the", "a", "there", "answer", "any", "by", "bye", "their".
In Trie structure, we have a field to store end of word marker, we call it isLeaf in below implementation. To count words, we need to simply traverse the Trie and count all nodes where isLeaf is set.
Implementation:
C++ // C++ implementation to count words in a trie #include <bits/stdc++.h> using namespace std; #define ARRAY_SIZE(a) sizeof(a)/sizeof(a[0]) // Alphabet size (# of symbols) #define ALPHABET_SIZE (26) // Converts key current character into index // use only 'a' through 'z' and lower case #define CHAR_TO_INDEX(c) ((int)c - (int)'a') // Trie node struct TrieNode { struct TrieNode *children[ALPHABET_SIZE]; // isLeaf is true if the node represents // end of a word bool isLeaf; }; // Returns new trie node (initialized to NULLs) struct TrieNode *getNode(void) { struct TrieNode *pNode = new TrieNode; pNode->isLeaf = false; for (int i = 0; i < ALPHABET_SIZE; i++) pNode->children[i] = NULL; return pNode; } // If not present, inserts key into trie // If the key is prefix of trie node, just // marks leaf node void insert(struct TrieNode *root, const char *key) { int length = strlen(key); struct TrieNode *pCrawl = root; for (int level = 0; level < length; level++) { int index = CHAR_TO_INDEX(key[level]); if (!pCrawl->children[index]) pCrawl->children[index] = getNode(); pCrawl = pCrawl->children[index]; } // mark last node as leaf pCrawl->isLeaf = true; } // Function to count number of words int wordCount(struct TrieNode *root) { int result = 0; // Leaf denotes end of a word if (root -> isLeaf) result++; for (int i = 0; i < ALPHABET_SIZE; i++) if (root -> children[i]) result += wordCount(root -> children[i]); return result; } // Driver int main() { // Input keys (use only 'a' through 'z' // and lower case) char keys[][8] = {"the", "a", "there", "answer", "any", "by", "bye", "their"}; struct TrieNode *root = getNode(); // Construct Trie for (int i = 0; i < ARRAY_SIZE(keys); i++) insert(root, keys[i]); cout << wordCount(root); return 0; } // Java implementation to count words in a trie public class Words_in_trie { // Alphabet size (# of symbols) static final int ALPHABET_SIZE = 26; // Trie node static class TrieNode { TrieNode[] children = new TrieNode[ALPHABET_SIZE]; // isLeaf is true if the node represents // end of a word boolean isLeaf; TrieNode(){ isLeaf = false; for (int i = 0; i < ALPHABET_SIZE; i++) children[i] = null; } }; static TrieNode root; // If not present, inserts key into trie // If the key is prefix of trie node, just // marks leaf node static void insert(String key) { int length = key.length(); TrieNode pCrawl = root; for (int level = 0; level < length; level++) { int index = key.charAt(level) - 'a'; if (pCrawl.children[index] == null) pCrawl.children[index] = new TrieNode(); pCrawl = pCrawl.children[index]; } // mark last node as leaf pCrawl.isLeaf = true; } // Function to count number of words static int wordCount(TrieNode root) { int result = 0; // Leaf denotes end of a word if (root.isLeaf) result++; for (int i = 0; i < ALPHABET_SIZE; i++) if (root.children[i] != null ) result += wordCount(root.children[i]); return result; } // Driver Program public static void main(String args[]) { // Input keys (use only 'a' through 'z' // and lower case) String keys[] = {"the", "a", "there", "answer", "any", "by", "bye", "their"}; root = new TrieNode(); // Construct Trie for (int i = 0; i < keys.length; i++) insert(keys[i]); System.out.println(wordCount(root)); } } // This code is contributed by Sumit Ghosh # Python implementation to count words in a trie # Alphabet size (# of symbols) from pickle import NONE ALPHABET_SIZE = 26 # Trie node class TrieNode: def __init__(self): # isLeaf is true if the node represents # end of a word self.isLeaf = False self.children = [None for i in range(ALPHABET_SIZE)] root = TrieNode() # If not present, inserts key into trie # If the key is prefix of trie node, just # marks leaf node def insert(key): length = len(key) pCrawl = root for level in range(length): index = ord(key[level]) - ord('a') if (pCrawl.children[index] == None): pCrawl.children[index] = TrieNode() pCrawl = pCrawl.children[index] # mark last node as leaf pCrawl.isLeaf = True # Function to count number of words def wordCount(root): result = 0 # Leaf denotes end of a word if (root.isLeaf == True): result += 1 for i in range(ALPHABET_SIZE): if (root.children[i] != None): result += wordCount(root.children[i]) return result # Driver Program # Input keys (use only 'a' through 'z' # and lower case) keys = ["the", "a", "there", "answer", "any", "by", "bye", "their"]; root = TrieNode() # Construct Trie for i in range(len(keys)): insert(keys[i]) print(wordCount(root)) # This code is contributed by shinjanpatra // C# implementation to count words in a trie using System; public class Words_in_trie { // Alphabet size (# of symbols) static readonly int ALPHABET_SIZE = 26; // Trie node public class TrieNode { public TrieNode[] children = new TrieNode[ALPHABET_SIZE]; // isLeaf is true if the node represents // end of a word public bool isLeaf; public TrieNode() { isLeaf = false; for (int i = 0; i < ALPHABET_SIZE; i++) children[i] = null; } }; static TrieNode root; // If not present, inserts key into trie // If the key is prefix of trie node, just // marks leaf node static void insert(String key) { int length = key.Length; TrieNode pCrawl = root; for (int level = 0; level < length; level++) { int index = key[level] - 'a'; if (pCrawl.children[index] == null) pCrawl.children[index] = new TrieNode(); pCrawl = pCrawl.children[index]; } // mark last node as leaf pCrawl.isLeaf = true; } // Function to count number of words static int wordCount(TrieNode root) { int result = 0; // Leaf denotes end of a word if (root.isLeaf) result++; for (int i = 0; i < ALPHABET_SIZE; i++) if (root.children[i] != null ) result += wordCount(root.children[i]); return result; } // Driver code public static void Main() { // Input keys (use only 'a' through 'z' // and lower case) String []keys = {"the", "a", "there", "answer", "any", "by", "bye", "their"}; root = new TrieNode(); // Construct Trie for (int i = 0; i < keys.Length; i++) insert(keys[i]); Console.WriteLine(wordCount(root)); } } /* This code contributed by PrinciRaj1992 */ <script> // JavaScript implementation to count words in a trie // Alphabet size (# of symbols) const ALPHABET_SIZE = 26; // Trie node class TrieNode { constructor(){ // isLeaf is true if the node represents // end of a word this.isLeaf = false; this.children = new Array(ALPHABET_SIZE).fill(null); } } let root = new TrieNode(); // If not present, inserts key into trie // If the key is prefix of trie node, just // marks leaf node function insert(key) { let length = key.length; let pCrawl = root; for (let level = 0; level < length; level++) { let index = key.charCodeAt(level) - 'a'.charCodeAt(0); if (pCrawl.children[index] == null) pCrawl.children[index] = new TrieNode(); pCrawl = pCrawl.children[index]; } // mark last node as leaf pCrawl.isLeaf = true; } // Function to count number of words function wordCount(root) { let result = 0; // Leaf denotes end of a word if (root.isLeaf) result++; for (let i = 0; i < ALPHABET_SIZE; i++) if (root.children[i] != null ) result += wordCount(root.children[i]); return result; } // Driver Program // Input keys (use only 'a' through 'z' // and lower case) let keys = ["the", "a", "there", "answer", "any", "by", "bye", "their"]; root = new TrieNode(); // Construct Trie for (let i = 0; i < keys.length; i++) insert(keys[i]); document.write(wordCount(root),"</br>"); // This code is contributed by shinjanpatra </script> Time complexity: O(n*k), where n is the number of words in the trie and k is the length of the longest word in the trie.
Auxiliary Space: O(n*k)