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Search in a trie Recursively

  • Last Updated : 22 Nov, 2021

Trie is an efficient information retrieval data structure. Using Trie, search complexities can be brought to an optimal limit (key length).
The task is to search a string in a Trie using recursion.
Examples : 
 

                                          root
                                         /  \    
                                         t   a     
                                         |   |     
                                         h   n     
                                         |   |  \  
                                         e   s   y  
                                      /  |   |
                                     i   r   w
                                     |   |   |
                                      r  e   e
                                             |
                                             r

Input : str = "anywhere"                                      
Output : not found

Input : str = "answer"                                      
Output : found

 

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Approach : 
Searching a key is similar to insertion operation, however, we only compare the characters and move down. The search can terminate due to the end of a string or lack of key in the trie. In the former case, if the endOfWord field of the last node is true, then the key exists in the trie. In the second case, the search terminates without examining all the characters of the key, since the key is not present in the trie. 
Below is the implementation of the above approach :
 

C++




// CPP program to search in a trie
#include <bits/stdc++.h>
using namespace std;
#define CHILDREN 26
#define MAX 100
 
// Trie node
struct trie {
    trie* child[CHILDREN];
    // endOfWord is true if the node represents
    // end of a word
    bool endOfWord;
};
 
// Function will return the new node(initialized to NULLs)
trie* createNode()
{
    trie* temp = new trie();
    temp->endOfWord = false;
    for (int i = 0; i < CHILDREN; i++) {
        // initially assign null to the all child
        temp->child[i] = NULL;
    }
    return temp;
}
/*function will insert the string in a trie recursively*/
void insertRecursively(trie* itr, string str, int i)
{
    if (i < str.length()) {
        int index = str[i] - 'a';
        if (itr->child[index] == NULL) {
 
            // Insert a new node
            itr->child[index] = createNode();
        }
        // Recursive call for insertion of a string
        insertRecursively(itr->child[index], str, i + 1);
    }
    else {
        // Make the endOfWord true which represents
        // the end of string
        itr->endOfWord = true;
    }
}
// Function call to insert a string
void insert(trie* itr, string str)
{
    // Function call with necessary arguments
    insertRecursively(itr, str, 0);
}
 
// Function to search the string in a trie recursively
bool searchRecursively(trie* itr, char str[], int i,
                                               int len)
{
    // When a string or any character
    // of a string is not found
    if (itr == NULL)
        return false;
 
    // Condition of finding string successfully
    if (itr->endOfWord == true && i == len - 1) {
        // Return true when endOfWord
        // of last node containes true
        return true;
    }
 
    int index = str[i] - 'a';
    // Recursive call and return
    // value of function call stack
    return searchRecursively(itr->child[index],
                                   str, i + 1, len);
}
 
// Function call to search the string
void search(trie* root, string str)
{
    char arr[str.length() + 1];
    strcpy(arr, str.c_str());
    // If string found
    if (searchRecursively(root, arr, 0, str.length() + 1))
        cout << "found" << endl;
 
    else {
        cout << "not found" << endl;
    }
}
 
// Driver code
int main()
{
    trie* root = createNode();
 
    // Function call to insert the string
    insert(root, "their");
    insert(root, "there");
    insert(root, "answer");
    insert(root, "any");
 
    // Function call to search the string
    search(root, "anywhere");
    search(root, "answer");
 
    return 0;
}

Java




// Java program to search in a trie
import java.util.*;
public class Main
{
    static int CHILDREN = 26;
     
    // Trie node
    static class trie  {
         
        public boolean endOfWord;
        public trie[] child;
         
        public trie()
        {
            endOfWord = false;
           
            // endOfWord is true if the node represents
            // end of a word
            child = new trie[CHILDREN];
        }
    }
     
    // Function will return the new node(initialized to NULLs)
    static trie createNode()
    {
        trie temp = new trie();
        temp.endOfWord = false;
        for (int i = 0; i < CHILDREN; i++)
        {
           
            // Initialise all child to the null, initially
            temp.child[i] = null;
        }
           
        // Return newly created node
        return temp;
    }
   
    // Function will insert the string in a trie recursively
    static void insertRecursively(trie itr, String str, int i)
    {
        if (i < str.length()) {
            int index = str.charAt(i) - 'a';
            if (itr.child[index] == null)
            {
               
                // Assigning a newly created node
                itr.child[index] = createNode();
            }
           
            // Recursive call for insertion
            // of a string in a trie
            insertRecursively(itr.child[index], str, i + 1);
        }
        else
        {
           
            // Make the endOfWord true which represents
            // the end of string
            itr.endOfWord = true;
        }
    }
    // Function call to insert a string
    static void insert(trie itr, String str)
    {
        // Function call with necessary arguments
        insertRecursively(itr, str, 0);
    }
      
    // Function to search the string in a trie recursively
    static boolean searchRecursively(trie itr, char[] str, int i, int len)
    {
        // When a string or any character
        // of a string is not found
        if (itr == null)
            return false;
       
        // Condition of finding string successfully
        if (itr.endOfWord == true && i == len - 1)
        {
           
            // Return true when endOfWord
            // of last node containes true
            return true;
        }
       
        int index = str[i] - 'a';
       
        // Recursive call and return
        // value of function call stack
        return searchRecursively(itr.child[index], str, i + 1, len);
    }
       
    // Function call to search the string
    static void search(trie root, String str)
    {
        char[] arr = new char[str.length() + 1];
        for(int i = 0; i < str.length(); i++)
        {
            arr[i] = str.charAt(i);
        }
        // If string found
        if (searchRecursively(root, arr, 0, str.length() + 1))
            System.out.println("found");
       
        else {
            System.out.println("not found");
        }
    }
     
    public static void main(String[] args) {
        trie root = createNode();
   
        // Function call to insert the string
        insert(root, "their");
        insert(root, "there");
        insert(root, "answer");
        insert(root, "any");
       
        // Function call to search the string
        search(root, "anywhere");
        search(root, "answer");
    }
}
 
// This code is contributed by suresh07.

Python3




# Python3 program to traverse in bottom up manner
CHILDREN = 26
MAX = 100
 
# Trie node
class trie:
 
    def __init__(self):
        self.child = [None for i in range(CHILDREN)]
         
        # endOfWord is true if the node represents
        # end of a word
        self.endOfWord = False
 
# Function will return the new node(initialized to NULLs)
def createNode():
 
    temp = trie()
    return temp
 
# Function will insert the string in a trie recursively
def insertRecursively(itr, str, i):
 
    if(i < len(str)):
     
        index = ord(str[i]) - ord('a')
         
        if(itr.child[index] == None ):
         
            # Insert a new node
            itr.child[index] = createNode();
         
        # Recursive call for insertion of string
        insertRecursively(itr.child[index], str, i + 1);
     
    else:
     
        # Make the endOfWord true which represents
        # the end of string
        itr.endOfWord = True;
     
# Function call to insert a string
def insert(itr, str):
 
    # Function call with necessary arguments
    insertRecursively(itr, str, 0);
  
# Function to search the string in a trie recursively
def searchRecursively(itr ,str, i, len):
 
    # When a string or any character
    # of a string is not found
    if (itr == None):
        return False
 
    # Condition of finding string successfully
    if (itr.endOfWord == True and i == len - 1):
         
        # Return true when endOfWord
        # of last node containes true
        return True
     
    index = ord(str[i]) - ord('a')
 
    # Recursive call and return
    # value of function call stack
    return searchRecursively(itr.child[index], str, i + 1, len)
 
# Function call to search the string
def search(root, str):
 
    arr = ['' for i in range(len(str) + 1)]
    arr = str
     
    # If string found
    if (searchRecursively(root, arr, 0, len(str) + 1)):
        print("found")
    else:
        print("not found")
 
# Driver code
if __name__=='__main__':
     
    root = createNode();
     
    # Function call to insert the string
    insert(root, "their");
    insert(root, "there");
    insert(root, "answer");
    insert(root, "any");
     
    # Function call to search the string
    search(root, "anywhere")
    search(root, "answer")
  
# This code is contributed by rutvik_56

C#




// C# program to search in a trie
using System;
class GFG {
     
    static int CHILDREN = 26;
     
    // Trie node
    class trie {
        
        public bool endOfWord;
        public trie[] child;
        
        public trie()
        {
            endOfWord = false;
            // endOfWord is true if the node represents
            // end of a word
            child = new trie[CHILDREN];
        }
    }
      
    // Function will return the new node(initialized to NULLs)
    static trie createNode()
    {
        trie temp = new trie();
        temp.endOfWord = false;
        for (int i = 0; i < CHILDREN; i++) {
            // Initialise all child to the null, initially
            temp.child[i] = null;
        }
          
        // Return newly created node
        return temp;
    }
    // Function will insert the string in a trie recursively
    static void insertRecursively(trie itr, string str, int i)
    {
        if (i < str.Length) {
            int index = str[i] - 'a';
            if (itr.child[index] == null) {
                // Assigning a newly created node
                itr.child[index] = createNode();
            }
            // Recursive call for insertion
            // of a string in a trie
            insertRecursively(itr.child[index], str, i + 1);
        }
        else {
            // Make the endOfWord true which represents
            // the end of string
            itr.endOfWord = true;
        }
    }
    // Function call to insert a string
    static void insert(trie itr, string str)
    {
        // Function call with necessary arguments
        insertRecursively(itr, str, 0);
    }
     
    // Function to search the string in a trie recursively
    static bool searchRecursively(trie itr, char[] str, int i, int len)
    {
        // When a string or any character
        // of a string is not found
        if (itr == null)
            return false;
      
        // Condition of finding string successfully
        if (itr.endOfWord == true && i == len - 1) {
            // Return true when endOfWord
            // of last node containes true
            return true;
        }
      
        int index = str[i] - 'a';
        // Recursive call and return
        // value of function call stack
        return searchRecursively(itr.child[index], str, i + 1, len);
    }
      
    // Function call to search the string
    static void search(trie root, string str)
    {
        char[] arr = new char[str.Length + 1];
        for(int i = 0; i < str.Length; i++)
        {
            arr[i] = str[i];
        }
        // If string found
        if (searchRecursively(root, arr, 0, str.Length + 1))
            Console.WriteLine("found");
      
        else {
            Console.WriteLine("not found");
        }
    }
 
  static void Main() {
    trie root = createNode();
  
    // Function call to insert the string
    insert(root, "their");
    insert(root, "there");
    insert(root, "answer");
    insert(root, "any");
  
    // Function call to search the string
    search(root, "anywhere");
    search(root, "answer");
  }
}
 
// This code is contributed by mukesh07.
Output: 
not found
found

 




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