Search in a trie Recursively

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

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 :

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// 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 inert 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, "thier");
    insert(root, "there");
    insert(root, "answer");
    insert(root, "any");
  
    // Function call to search the string
    search(root, "anywhere");
    search(root, "answer");
  
    return 0;
}

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Output:

not found
found


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Improved By : Akanksha_Rai