C++ Program to Implement Trie

Here we shall discuss a C++ Program to implement Trie. It is a tree based data structure, used for efficient retrieval of a key in a large data-set of strings.

Functions and pseudocodes

Begin
function insert() :
   If key not present, inserts key into trie. If the key is prefix of trie node, just mark leaf node.
End
Begin
function deleteNode()
   If tree is empty then return null.
   If last character of the key is being processed,
      then that node will be no more end of string after deleting it.
      If given key is not prefix of any other string, then delete it and set root = NULL.
   If key is not the last character,
      Then recur for the child which will be obtained by using ASCII value.
   If root does not have any child left and it is not end of another word,
      Then delete it and set root = NULL.
End

Example

#include <bits/stdc++.h>
using namespace std;
const int ALPHA_SIZE = 26;

struct Trie {
   struct Trie *child[ALPHA_SIZE];
   bool endofstring; //It is true if node represents end of word.
};
struct Trie *createNode(void) //creation of new node {
   struct Trie *tNode = new Trie;
   tNode->endofstring = false;
   for (int i = 0; i < ALPHA_SIZE; i++)
      tNode->child[i] = NULL;
   return tNode;
}
void insert(struct Trie *root, string key) {
   struct Trie *curr = root;
   for (int i = 0; i < key.length(); i++) {
      int index = key[i] - 'A';
      if (!curr->child[index])
         curr->child[index] = createNode();
         curr = curr->child[index];
   }
   curr->endofstring= true; //last node as leaf
}
bool search(struct Trie *root, string key) { //check if key is present in trie. If present returns true
   struct Trie *curr = root;
   for (int i = 0; i < key.length(); i++) {
      int index = key[i] - 'A';
      if (!curr->child[index])
         return false;
      curr = curr->child[index];
   }
   return (curr != NULL && curr->endofstring);
}
bool isEmpty(Trie* root) //check if root has children or not {
   for (int i = 0; i < ALPHA_SIZE; i++)
   if (root->child[i])
   return false;
   return true;
}
Trie* deletion(Trie* root, string key, int depth = 0) {
   //If tree is empty return null.
   if (!root)
   return NULL;
   if (depth == key.size()) { //If last character of key is being processed,
      if (root->endofstring)
         root->endofstring = false; //then that node will be no more end of string after deleting it.
      if (isEmpty(root)) { //If given key is not prefix of any other string,
         delete (root);
         root = NULL;
      }
   return root;
   }
   //If key not last character,
   int index = key[depth] - 'A';
   root->child[index] =
   deletion(root->child[index], key, depth + 1); //Then recur for the child which will be obtained by using ASCII value.
   if (isEmpty(root) && root->endofstring == false) { //If root does not have any child leftand it is not end of another word
      delete (root);
      root = NULL;
   }
   return root;
}
int main() {
   string inputs[] = {"HELLOWORLD","HI","BYE", "THE","THENA"}; // Input keys ( only A to Z in upper case)
   int n = sizeof(inputs)/sizeof(inputs[0]);
   struct Trie *root = createNode();
   for (int i = 0; i < n; i++)
   insert(root, inputs[i]);
   search(root, "HELLOWORLD")? cout << "Key is Found\n" :
   cout << "Key is not Found\n";
   search(root, "HE")? cout << "Key is Found\n" :
   cout << "Key is not Found\n";
   deletion(root, "THEN")? cout << "Key is deleted\n" :
   cout << "Key is not Deleted\n";
   return 0;
}

Output

Key is Found
Key is not Found
Key is deleted