Strings from an array which are not prefix of any other string

Given an array arr[] of strings, the task is to print the strings from the array which are not prefix of any other string from the same array.


Input: arr[] = {“apple”, “app”, “there”, “the”, “like”}
Here “app” is a prefix of “apple”
Hence, it is not printed and
“the” is a prefix of “there”

Input: arr[] = {“a”, “aa”, “aaa”, “aaaa”}

Naive approach: For every string of the array, we check if it is prefix of any other string. If it is then don’t display it.

Efficient approach: We pick strings from array one by one and insert it into Trie. Then there are two cases for the insertion of the string:

  1. While inserting if we found that the picked string is a prefix of an already inserted string then we don’t insert this string into the Trie.
  2. If a prefix is inserted first into the Trie and afterwards we find that the string is a prefix of some word then we simply make isEndOfWord = false for that particular node.

After constructing the Trie, we traverse it and display all the words in the Trie.

Below is the implementation of the above approach:





// C++ implementation of the approach
#include <bits/stdc++.h>
using namespace std;
const int ALPHABET_SIZE = 26;
// Trie node
struct TrieNode {
    struct TrieNode* children[ALPHABET_SIZE];
    // isEndOfWord is true if the node represents
    // end of a word
    bool isEndOfWord;
// Returns new trie node (initialized to NULLs)
struct TrieNode* getNode(void)
    struct TrieNode* pNode = new TrieNode;
    pNode->isEndOfWord = false;
    for (int i = 0; i < ALPHABET_SIZE; i++)
        pNode->children[i] = NULL;
    return pNode;
// Function to insert a string into trie
void insert(struct TrieNode* root, string key)
    struct TrieNode* pCrawl = root;
    for (int i = 0; i < key.length(); i++) {
        int index = key[i] - 'a';
        if (!pCrawl->children[index])
            pCrawl->children[index] = getNode();
        // While inerting a word make
        // each isEndOfWord as false
        pCrawl->isEndOfWord = false;
        pCrawl = pCrawl->children[index];
    int i;
    // Check if this word is prefix of
    // some already inserted word
    // If it is then don't insert this word
    for (i = 0; i < 26; i++) {
        if (pCrawl->children[i]) {
    // If present word is not prefix of
    // any other word then insert it
    if (i == 26) {
        pCrawl->isEndOfWord = true;
// Function to display words in Trie
void display(struct TrieNode* 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 (root->isEndOfWord) {
        str[level] = '\0';
        cout << str << endl;
    int i;
    for (i = 0; i < ALPHABET_SIZE; i++) {
        // If NON NULL child is found
        // add parent key to str and
        // call the display function recursively
        // for child node
        if (root->children[i]) {
            str[level] = i + 'a';
            display(root->children[i], str, level + 1);
// Driver code
int main()
    string keys[] = { "apple", "app", "there",
                      "the", "like" };
    int n = sizeof(keys) / sizeof(string);
    struct TrieNode* root = getNode();
    // Construct trie
    for (int i = 0; i < n; i++)
        insert(root, keys[i]);
    char str[100];
    display(root, str, 0);
    return 0;




Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.

My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using or mail your article to See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Improved By : ManasChhabra2