Implement Trie (Prefix Tree)

Implement a trie with 

insert

, 

search

,
and 

startsWith

 methods.

Note:

You may assume that all inputs are consist of lowercase letters 

a-z

.

class TrieNode {
public:
// Initialize your data structure here.
TrieNode(){
m_isWord = false;
for (int i = 0; i < 26; ++i){
next[i] = NULL;
}
}
void setIsWord(bool isWord){
m_isWord = isWord;
}
bool getIsWord(void){
return m_isWord;
}
public:
bool m_isWord;
TrieNode* next[26];
};

class Trie {
public:
Trie() {
root = new TrieNode();
}

// Inserts a word into the trie.
void insert(string word) {
int len = word.length();
if (len == 0) return;
TrieNode* p = root;
for (int i = 0; i < len; ++i){
if (p->next[word[i] - 'a'] == NULL){
p->next[word[i] - 'a'] = new TrieNode();
p = p->next[word[i] - 'a'];
}
else{
p = p->next[word[i] - 'a'];
}
}
p->setIsWord(true);
}

// Returns if the word is in the trie.
bool search(string word) {
int len = word.length();
if (len == 0) return true;
bool ans = false;
TrieNode* p = root;
for (int i = 0; i < len; ++i){
if (p->next[word[i] - 'a'] == NULL){
return false;
}
else{
p = p->next[word[i] - 'a'];
}
}
return p->getIsWord();
}

// Returns if there is any word in the trie
// that starts with the given prefix.
bool startsWith(string prefix) {
int len = prefix.length();
if (len == 0) return true;
bool ans = false;
TrieNode* p = root;
for (int i = 0; i < len; ++i){
if (p->next[prefix[i] - 'a'] == NULL){
return false;
}
else{
p = p->next[prefix[i] - 'a'];
}
}
return true;
}

private:
TrieNode* root;
};