Print Strings In Reverse Dictionary Order Using Trie

Trie is an efficient information retrieval data structure. Using Trie, search complexities can be brought to an optimal limit.

Given an array of strings. The task is to print all strings in reverse dictionary order using Trie. If there are duplicates in the input array, we need to print them only once.

Examples:

Input: str = {"cat", "there", "caller", "their", "calling"}
Output: there
        their
        cat
        calling
        caller

                                       root
                                      /     \    
                                     c       t     
                                     |       |     
                                     a       h     
                                     | \     |     
                                     l  t    e      
                                     |       |  \
                                     l       i   r
                                     | \     |   |
                                     e  i    r   e
                                     |  |
                                     r  n
                                        |
                                        g 

Input: str = {"Candy", "cat", "Caller", "calling"}
Output: cat
        candy
        calling
        caller
                                        root
                                         |    
                                         c            
                                         |            
                                         a            
                                      /   | \        
                                     l    n  t       
                                     |    |       
                                     l    d       
                                     | \  |      
                                     e  i y      
                                     |  |
                                     r  n
                                        |
                                        g

Approach:

To solve the problem mentioned above, first, construct a Trie using all strings then print a string of rightmost subtree from top to bottom then print a string of second right subtree from top to bottom then print for third right subtree and so on. It is similar to preorder traversal of a tree from right to left.

Below is the implementation of the above approach:

// C++ programm to print array of string 
// in reverse dictionary order using 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 NULL 
trie* createNode() 
{ 
    trie* temp = new trie(); 
  
    temp->endOfWord = false; 
  
    for (int i = 0; i < CHILDREN; i++) { 
  
        // Initialize 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) { 
  
            // Create 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 
void insert(trie* itr, string str) 
{ 
    // Function call with necessary arguments 
    insertRecursively(itr, str, 0); 
} 
  
// Function to check whether the node is leaf or not 
bool isLeafNode(trie* root) 
{ 
    return root->endOfWord != false; 
} 
  
// Function to display the content of trie 
void displayContent(trie* root, char str[], int level) 
{ 
  
    // If node is leaf node, it indicates end 
    // of string, so a null character is added 
    // and string is displayed 
    if (isLeafNode(root)) { 
        // Assign a null character in temporary string 
        str[level] = '\0'; 
        cout << str << endl; 
    } 
  
    for (int i = CHILDREN - 1; i >= 0; i--) { 
  
        // check if NON NULL child is found 
        // add parent key to str and 
        // call the display function recursively 
        // for child node 
        if (root->child[i]) { 
            str[level] = i + 'a'; 
            displayContent(root->child[i], str, level + 1); 
        } 
    } 
} 
  
// Function call for displaying content 
void display(trie* itr) 
{ 
    int level = 0; 
  
    char str[MAX]; 
  
    displayContent(itr, str, level); 
} 
  
// Driver code 
int main() 
{ 
    trie* root = createNode(); 
    insert(root, "their"); 
    insert(root, "there"); 
    insert(root, "answer"); 
    insert(root, "any"); 
  
    /* After inserting strings, trie will look like  
                                        root  
                                        / \  
                                        a     t      
                                        |     |      
                                        n     h      
                                        | \ |  
                                        s y e      
                                        |     | \  
                                        w     i r  
                                        |     | |  
                                        e     r e  
                                        |      
                                        r  
    */
  
    display(root); 
  
    return 0; 
} 

Output:

there
their
any
answer

Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.

My Personal Notes

Recommended Posts: