Ternary Search Tree Implementation in C++

A Ternary Search Tree is a trie which leverages concepts of Binary Search Tree as well. A Ternary Search Tree is as memory efficient as Binary Search Trees and time efficient as a Trie.

It is an efficient data structure to store and search large number of strings.

A node in a Ternary Search Tree comprises of these fields :

• Left pointer - Points to Ternary Search Tree containing all strings alphabetically lesser than current node's data
• Right pointer - Points to Ternary Search Tree containing all strings alphabetically greater than current node's data
• Equal pointer - Points to Ternary Search Tree containing all strings alphabetically equal to current node's data
• End of string flag - Flag indicating the end of string
• Data - Actual data in the form of single character

Ternary Search Tree Node

For example, consider adding these strings in the same order into a Ternary Search Tree :

1. "Lead"
2. "Leader"
3. "Leads"
4. "Late"
5. "State"

Let's build a visualization of ternary search tree out of above data :

1. "Lead"
   
2. "Leader"
   
   
3. "Leads"
   
   
4. "Late"
   
   
5. "State"
   

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//TST.h #ifndef TST_H #define TST_H //#define DEBUG_PROGRAM_MEMORY //Node of a Ternary Search Tree typedef struct TSTNode{  char data; //Actual data stored in form of character  bool bEOS; //flag marking end of string  struct TSTNode* left;   //All character data less than this node  struct TSTNode* eq;  //All character data equal to this node  struct TSTNode* right; //All character data greater than this node }TSTNode; //Inserts a string in the TST TSTNode* Insert(TSTNode* root, char* str); //Prints all strings in the TST void PrintAllStringsInTST(TSTNode* root); //Gets the length of maximum length string in TST int MaxLenStringLen(TSTNode *root); //Deleted the complete TST void DeleteTST(TSTNode *root); //Search a pattern in TST bool SearchTST(TSTNode *root, char* pattern); //Prints #ifdef DEBUG_PROGRAM_MEMORY #include <map> static std::map<TSTNode*, char> mem_addrs; void CheckTSTMem(); #endif #endif

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//TST.cpp #include <iostream> #define DEBUG_PROGRAM_MEMORY #include "TST.h" #include <cstdlib> #include <utility> #define MAX_LEN 1024 #define MAX( a, b, c ) ((a)>(b) ? ((a)>(c) ? (a):(c)) : ( (b)>(c) ? (b):(c) )) TSTNode* Insert(TSTNode* root, char* str) {  if(root == NULL)  {   root = (TSTNode*)malloc(sizeof(TSTNode));   if(root == NULL)   {    std::cout<<"Memory allocation failed"<<std::endl;    return NULL;   }   //Insert first character of string in the root node   root->data = *str; #ifdef DEBUG_PROGRAM_MEMORY   mem_addrs.insert(std::make_pair(root, root->data)); #endif   root->bEOS = false;   root->left = root->eq = root->right = NULL;  }     if(*str  < root->data)   root->left = Insert(root->left, str);  else if (*str == root->data)  {   if(*(str + 1))    root->eq = Insert(root->eq, str + 1);   else    root->bEOS = true;  }  else   root->right = Insert(root->right, str);     return root; } //Helper to print the strings in TST static void PrintHelper(TSTNode* root, char* buffer, int depth) {  if (root)  {   // Traverse the left subtree   PrintHelper(root->left, buffer, depth);   buffer[depth] = root->data;   //Once end of string flag is encountered, print the string   if (root->bEOS)   {    buffer[depth + 1] = '\0';    std::cout<< buffer << std::endl;   }   // Traverse the middle subtree   PrintHelper(root->eq, buffer, depth + 1);   // Traverse the right subtree   PrintHelper(root->right, buffer, depth);  } } // Function to print TST's strings void PrintAllStringsInTST(TSTNode* root) {  char buffer[MAX_LEN];  PrintHelper(root, buffer, 0); } bool SearchTST(TSTNode *root, char* pattern) {  while (root != NULL)  {   if (*pattern < root->data)    root = root->left;   else if (*pattern == root->data)   {    //If end of string flag is found and the pattern length is also exhausted,    //we can safely say that the pattern is present in the TST    if (root->bEOS && *(pattern + 1) == '\0')     return true;    pattern++;    root = root->eq;   }   else    root = root->right;  }  return false; } //Function to determine largest int MaxLenStringLen(TSTNode *root) {  if (root == NULL)   return 0;  int leftLen = MaxLenStringLen(root->left);  int middleLen = MaxLenStringLen(root->eq) + 1;  int rightLen = MaxLenStringLen(root->right);  return MAX( leftLen, middleLen, rightLen); } void DeleteTST(TSTNode *root) {  TSTNode *tmp = root;  if (tmp)  {   DeleteTST(tmp->left);   DeleteTST(tmp->eq);   DeleteTST(tmp->right); #ifdef DEBUG_PROGRAM_MEMORY   mem_addrs.erase(tmp); #endif   delete tmp;  } } #ifdef DEBUG_PROGRAM_MEMORY void CheckTSTMem() {  std::map<TSTNode*, char>::iterator itr = mem_addrs.begin();  if (mem_addrs.size() == 0)  {   std::cout << "No memory leaks";   return;  }  while (itr != mem_addrs.end())  {   std::cout << "Memory address " << itr->first<< " for \"" << itr->second << "\" has not been deallocated" << std::endl;   ++itr;  } } #endif

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//Main.cpp #include <iostream> #include "TST.h" int main(int argc, char** argv) {     TSTNode *root = NULL;  root = Insert(root, "boats");  root = Insert(root, "boat");  root = Insert(root, "bat");  root = Insert(root, "bats");  root = Insert(root, "stages");  PrintAllStringsInTST(root);  std::cout << "Maximum length string in this TST is of size "<< MaxLenStringLen(root) << std::endl;  char *str = "hello";  char *str1 = "bat";  if (SearchTST(root, str) == false)   std::cout << "\""<<str<<"\" not found in TST" << std::endl;  else   std::cout << "\"" << str << "\" is present in TST" << std::endl;  if (SearchTST(root, str1) == false)   std::cout << "\"" << str << "\" not found in TST" << std::endl;  else   std::cout << "\"" << str1 << "\" is present in TST" << std::endl;  DeleteTST(root); #ifdef DEBUG_PROGRAM_MEMORY  CheckTSTMem(); #endif     return 0; }