Implementation of a trie tree

Trie tree implementation code:

// Max branch number. Such as 26 for lower case letter set, 10 for digit character set.const int MAX_BRANCH_NUM = 26;// Node of Trie Tree        class CTrieNode{public:CTrieNode(){nPrefixCount = 0;nWordCount = 0;memset(next, NULL, sizeof(next));}public:int nPrefixCount;    // Count of prefix in the Trie Treeint nWordCount;      // Count of word in the Trie TreeCTrieNode* next[MAX_BRANCH_NUM];  // Point to all the nodes in the next level};// Trie Tree classclass CTrieTree{public:CTrieTree();    // Constructor~CTrieTree();   // Destructorint GetIndex(char ch) const;           // Get the index of 'ch' in the 'next' arraybool CheckWord(const char *s) const;   // Check if there is illegal characterbool InsertWord(const char *s) const;  // Insert a wordint SearchPrefix(const char *s) const; // Search the count of a prefixint SearchWord(const char *s) const;   // Search the count of a wordbool DeleteWord(const char *s) const;  // Delete a wordprivate:void FreeTreeNodes(CTrieNode * root);  // Free those tree nodesprivate:CTrieNode *pRoot; // Root node pointer of Trie Tree};// ConstructorCTrieTree::CTrieTree(){pRoot = new CTrieNode; }// DestructorCTrieTree::~CTrieTree(){FreeTreeNodes(pRoot);}// Get the index of 'ch' in the 'next' arrayint CTrieTree::GetIndex(char ch) const{// This is for lower case letter setreturn ch - 'a';}// Check if there is illegal character in the wordbool CTrieTree::CheckWord(const char *s) const{// This is for lower case letter setfor(int i = 0; s[i] != '\0'; i++)if(s[i] < 'a' || s[i] > 'z')return false;return true;}// Insert a wordbool CTrieTree::InsertWord(const char *s) const{// Can't insert a null string or an word containing illegal characterif((s[0] == '\0') || (CheckWord(s)== false))return false;CTrieNode * pCurrent = pRoot;int i = 0;while(1){int nIndex = GetIndex(s[i]);if(pCurrent->next[nIndex] == NULL)pCurrent->next[nIndex] = new CTrieNode;pCurrent = pCurrent->next[nIndex];pCurrent->nPrefixCount++;i++;if(s[i] == '\0'){pCurrent->nWordCount++;break;}}return true;};// Search the count of a prefix in the Trie Treeint CTrieTree::SearchPrefix(const char *s) const{// There are no null prefix or a prefix containing illegal characterif((s[0] == '\0') || (CheckWord(s)== false))return 0;CTrieNode * pCurrent = pRoot;int i = 0;while(1){int nIndex = GetIndex(s[i]);pCurrent = pCurrent->next[nIndex];if((pCurrent == NULL) || (pCurrent->nPrefixCount == 0))return 0;i++;if(s[i] == '\0')return pCurrent->nPrefixCount;}}// Search the count of a word in the Trie Treeint CTrieTree::SearchWord(const char *s) const{// There are no null word or a word containing illegal characterif((s[0] == '\0') || (CheckWord(s)== false))return 0;CTrieNode * pCurrent = pRoot;int i = 0;while(1){int nIndex = GetIndex(s[i]);pCurrent = pCurrent->next[nIndex];if((pCurrent == NULL) || (pCurrent->nPrefixCount == 0))return 0;i++;if(s[i] == '\0')return pCurrent->nWordCount;}}// Delete a wordbool CTrieTree::DeleteWord(const char *s) const{if(!SearchWord(s))return false;CTrieNode * pCurrent = pRoot;int i = 0;while(1){int nIndex = GetIndex(s[i]);pCurrent = pCurrent->next[nIndex];pCurrent->nPrefixCount--;i++;if(s[i] == '\0'){pCurrent->nWordCount--;break;}}return true;}// Free those tree nodesvoid CTrieTree::FreeTreeNodes(CTrieNode * pRoot){if(pRoot == NULL)return;for(int i = 0; i < MAX_BRANCH_NUM; i++)FreeTreeNodes(pRoot->next[i]);free(pRoot);pRoot = NULL;}