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

• Difficulty Level : Medium
• Last Updated : 15 Feb, 2021

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.
Examples:

Input: arr[] = {“apple”, “app”, “there”, “the”, “like”}
Output:
apple
like
there
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”}
Output:
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:

## CPP

 `// C++ implementation of the approach``#include ``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]) {``            ``break``;``        ``}``    ``}``    ``// 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;``    ``display(root, str, 0);` `    ``return` `0;``}`

## Java

 `// Java implementation of the approach``import` `java.util.Arrays;``class` `GFG``{``  ``static` `final` `int` `ALPHABET_SIZE = ``26``;` `  ``// Trie node``  ``static` `class` `TrieNode``  ``{``    ``TrieNode[] children;` `    ``// isEndOfWord is true if the node represents``    ``// end of a word``    ``boolean` `isEndOfWord;``    ``TrieNode()``    ``{``      ``this``.children = ``new` `TrieNode[ALPHABET_SIZE];``    ``}``  ``}` `  ``// Returns new trie node (initialized to NULLs)``  ``static` `TrieNode getNode()``  ``{``    ``TrieNode pNode = ``new` `TrieNode();``    ``pNode.isEndOfWord = ``false``;``    ``Arrays.fill(pNode.children, ``null``);``    ``return` `pNode;``  ``}` `  ``// Function to insert a String into trie``  ``static` `void` `insert(TrieNode root, String key)``  ``{``    ``TrieNode pCrawl = root;` `    ``for` `(``int` `i = ``0``; i < key.length(); i++)``    ``{``      ``int` `index = key.charAt(i) - ``'a'``;``      ``if` `(pCrawl.children[index] == ``null``)``        ``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] != ``null``)``      ``{``        ``break``;``      ``}``    ``}` `    ``// 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``  ``static` `void` `display(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'``;``      ``System.out.println(str);``    ``}` `    ``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] != ``null``)``      ``{``        ``str[level] = (``char``) (i + ``'a'``);``        ``display(root.children[i], str, level + ``1``);``      ``}``    ``}``  ``}` `  ``// Driver code``  ``public` `static` `void` `main(String[] args)``  ``{` `    ``String keys[] = { ``"apple"``, ``"app"``, ``"there"``, ``"the"``, ``"like"` `};``    ``int` `n = keys.length;``    ``TrieNode root = getNode();` `    ``// Conclass trie``    ``for` `(``int` `i = ``0``; i < n; i++)``      ``insert(root, keys[i]);``    ``char``[] str = ``new` `char``[``100``];``    ``display(root, str, ``0``);``  ``}``}` `// This code is contributed by sanjeev2552`
Output:
```apple
like
there```

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