Sorting array of strings (or words) using Trie

Given an array of strings, print them in alphabetical (dictionary) order. If there are duplicates in input array, we need to print them only once.

Examples: 

Input : "abc", "xy", "bcd"
Output : abc bcd xy         

Input : "geeks", "for", "geeks", "a", "portal", 
        "to", "learn", "can", "be", "computer", 
        "science", "zoom", "yup", "fire", "in", "data"
Output : a be can computer data fire for geeks
         in learn portal science to yup zoom

Trie is an efficient data structure used for storing data like strings. To print the string in alphabetical order we have to first insert in the trie and then perform preorder traversal to print in alphabetical order.

Implementation:

CPP

// C++ program to sort an array of strings
// using Trie
#include <bits/stdc++.h>
using namespace std;

const int MAX_CHAR = 26;

struct Trie {

    // index is set when node is a leaf
    // node, otherwise -1;
    int index;

    Trie* child[MAX_CHAR];

    /*to make new trie*/
    Trie()
    {
        for (int i = 0; i < MAX_CHAR; i++)
            child[i] = NULL;
        index = -1;
    }
};

/* function to insert in trie */
void insert(Trie* root, string str, int index)
{
    Trie* node = root;

    for (int i = 0; i < str.size(); i++) {

        /* taking ascii value to find index of
          child node */
        char ind = str[i] - 'a';

        /* making new path if not already */
        if (!node->child[ind])
            node->child[ind] = new Trie();

        // go to next node
        node = node->child[ind];
    }

    // Mark leaf (end of word) and store
    // index of word in arr[]
    node->index = index;
}

/* function for preorder traversal */
bool preorder(Trie* node, string arr[])
{
    if (node == NULL)
        return false;

    for (int i = 0; i < MAX_CHAR; i++) {
        if (node->child[i] != NULL) {

            /* if leaf node then print key*/
            if (node->child[i]->index != -1)
                cout << arr[node->child[i]->index] << endl;

            preorder(node->child[i], arr);
        }
    }
}

void printSorted(string arr[], int n)
{
    Trie* root = new Trie();

    // insert all keys of dictionary into trie
    for (int i = 0; i < n; i++)
        insert(root, arr[i], i);

    // print keys in lexicographic order
    preorder(root, arr);
}

// Driver code
int main()
{
    string arr[] = { "abc", "xy", "bcd" };
    int n = sizeof(arr) / sizeof(arr[0]);
    printSorted(arr, n);
    return 0;
}

Java

// Java program to sort an array of strings using Trie

// Author : Rohit Jain
// GFG user_id : @rj03012002

import java.util.*;

public class GFG {

    // Alphabet size
    static final int MAX_CHAR = 26;

    // trie node
    static class Trie {

        // index is set when node is a leaf
        // node, otherwise -1;
        int index;

        Trie child[] = new Trie[MAX_CHAR];

        /*to make new trie*/
        Trie()
        {

            for (int i = 0; i < MAX_CHAR; i++)
                child[i] = null;
            index = -1;
        }
    }

    /* function to insert in trie */
    static void insert(Trie root, String str, int index)
    {

        Trie node = root;

        for (int i = 0; i < str.length(); i++) {
            /* taking ascii value to find index of
          child node */
            int ind = str.charAt(i) - 'a';

            /* making new path if not already */
            if (node.child[ind] == null)
                node.child[ind] = new Trie();

            // go to next node
            node = node.child[ind];
        }

        // Mark leaf (end of word) and store
        // index of word in arr[]
        node.index = index;
    }

    /* function for preorder traversal */
    static boolean preorder(Trie node, String arr[])
    {

        if (node == null) {

            return false;
        }

        for (int i = 0; i < MAX_CHAR; i++) {

            if (node.child[i] != null) {

                /* if leaf node then print key*/
                if (node.child[i].index != -1) {

                    System.out.print(
                        arr[node.child[i].index] + " ");
                }

                preorder(node.child[i], arr);
            }
        }
        return false;
    }

    static void printSorted(String arr[], int n)
    {

        Trie root = new Trie();

        // insert all keys of dictionary into trie
        for (int i = 0; i < n; ++i) {

            insert(root, arr[i], i);
        }

        // print keys in lexicographic order
        preorder(root, arr);
    }

    public static void main(String[] args)
    {

        String arr[] = { "abc", "xy", "bcd" };

        int n = arr.length;

        printSorted(arr, n);
    }
}

Python3

# Python3 program to sort an array of strings
# using Trie

MAX_CHAR = 26

class Trie:

    # index is set when node is a leaf
    # node, otherwise -1;
    # to make new trie
    def __init__(self):
        self.child = [None for i in range(MAX_CHAR)]
        self.index = -1


# def to insert in trie
def insert(root,str,index):

    node = root

    for i in range(len(str)):

        # taking ascii value to find index of
        # child node
        ind = ord(str[i]) - ord('a')

        # making new path if not already
        if (node.child[ind] == None):
            node.child[ind] = Trie()

        # go to next node
        node = node.child[ind]


    # Mark leaf (end of word) and store
    # index of word in arr[]
    node.index = index


# function for preorder traversal
def preorder(node, arr):

    if (node == None):
        return False

    for i in range(MAX_CHAR):
        if (node.child[i] != None):

            # if leaf node then print key
            if (node.child[i].index != -1):
                print(arr[node.child[i].index])

            preorder(node.child[i], arr)



def printSorted(arr,n):

    root = Trie()

    # insert all keys of dictionary into trie
    for i in range(n):
        insert(root, arr[i], i)

    # print keys in lexicographic order
    preorder(root, arr)


# Driver code

arr = [ "abc", "xy", "bcd" ]
n = len(arr)
printSorted(arr, n)

# This code is contributed by shinjanpatra

C#

// C# program to sort an array of strings using Trie
using System;

class GFG
{
    static int MAX_CHAR = 26;

    // trie node
    public class Trie
    {
        // index is set when node is a leaf node, otherwise -1
        public int index;

        public Trie[] child = new Trie[MAX_CHAR];

        // constructor to make a new trie node
        public Trie()
        {
            for (int i = 0; i < MAX_CHAR; i++)
                child[i] = null;
            index = -1;
        }
    }

    /* function to insert in trie */
     static void Insert(Trie root, string str, int index)
    {
        Trie node = root;

        for (int i = 0; i < str.Length; i++)
        {
            /* taking ASCII value to find the index of the child node */
            int ind = str[i] - 'a';

            /* making a new path if not already */
            if (node.child[ind] == null)
                node.child[ind] = new Trie();

            // go to the next node
            node = node.child[ind];
        }

        // mark the leaf node (end of the word) and store the index of the word in arr[]
        node.index = index;
    }

    /* function for preorder traversal */
    static void Preorder(Trie node, string[] arr)
    {
        if (node == null)
        {
            return;
        }

        for (int i = 0; i < MAX_CHAR; i++)
        {
            if (node.child[i] != null)
            {
                /* if leaf node, then print the key */
                if (node.child[i].index != -1)
                {
                    Console.WriteLine(arr[node.child[i].index] + " ");
                }

                Preorder(node.child[i], arr);
            }
        }
    }

    static void PrintSorted(string[] arr, int n)
    {
        Trie root = new Trie();

        // insert all keys of the dictionary into the trie
        for (int i = 0; i < n; i++)
        {
            Insert(root, arr[i], i);
        }

        // print the keys in lexicographic order
        Preorder(root, arr);
    }

    static void Main(string[] args)
    {
        string[] arr = { "abc", "xy", "bcd" };
        int n = arr.Length;

        PrintSorted(arr, n);
    }
}

// This code is contributed by Aman Kumar.

Javascript

<script>

// JavaScript program to sort an array of strings
// using Trie

const MAX_CHAR = 26;

class Trie {

    // index is set when node is a leaf
    // node, otherwise -1;
    /*to make new trie*/
    constructor()
    {
        this.child = new Array(MAX_CHAR).fill(null);
        this.index = -1;
    }
}

/* function to insert in trie */
function insert(root,str,index)
{
    let node = root;

    for (let i = 0; i < str.length; i++) {

        /* taking ascii value to find index of
        child node */
        let ind = str.charCodeAt(i) - 'a'.charCodeAt(0);

        /* making new path if not already */
        if (node.child[ind] == null)
            node.child[ind] = new Trie();

        // go to next node
        node = node.child[ind];
    }

    // Mark leaf (end of word) and store
    // index of word in arr[]
    node.index = index;
}

/* function for preorder traversal */
function preorder(node, arr)
{
    if (node == null)
        return false;

    for (let i = 0; i < MAX_CHAR; i++) {
        if (node.child[i] != null) {

            /* if leaf node then print key*/
            if (node.child[i].index != -1)
                document.write(arr[node.child[i].index],"</br>");

            preorder(node.child[i], arr);
        }
    }
}

function printSorted(arr,n)
{
    let root = new Trie();

    // insert all keys of dictionary into trie
    for (let i = 0; i < n; i++)
        insert(root, arr[i], i);

    // print keys in lexicographic order
    preorder(root, arr);
}

// Driver code

let arr = [ "abc", "xy", "bcd" ];
let n = arr.length;
printSorted(arr, n);

// This code is contributed by shinjanpatra

</script>

Output

abc
bcd
xy

Time Complexity: O(n*m) where n is the length of the array and m is the length of the longest word.
Auxiliary Space: O(n*m)

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