# Insertion 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).

Given multiple strings. The task is to insert the string in a Trie using recursion.

Examples:

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

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 : caller
calling
candy
cat
root
|
c
|
a
/   | \
l    n  t
|    |
l    d
| \  |
e  i y
|  |
r  n
|
g
```

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: An efficient approach is to treat every character of the input key as an individual trie node and insert it into the trie. Note that the children are an array of pointers (or references) to next level trie nodes. The key character acts as an index into the array of children. If the input key is new or an extension of the existing key, we need to construct non-existing nodes of the key, and mark end of the word for the last node. If the input key is a prefix of the existing key in Trie, we simply mark the last node of the key as the end of a word. The key length determines Trie depth.

Below is the implementation of the above approach:

 `#include ` `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 ; ichild[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 ) ` `        ``{ ` `                        ``//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 = 0; i < CHILDREN; i++) ` `    ``{ ` `        ``// 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]; ` ` `  `    ``// Function call with necessary arguments ` `    ``displayContent(itr, str, level); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``trie *root = createNode(); ` `    ``insert(root, ``"thier"``);  ` `    ``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:

```answer
any
there
their```

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 contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. 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 : Akanksha_Rai