[LeetCode] 208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.
• All inputs are guaranteed to be non-empty strings.

  class TrieNode {
  public:
      TrieNode *child[26];
      bool isWord;
      TrieNode(): isWord(false) {
          for (auto &a : child) a = nullptr;
      }
      
  };
  class Trie {
  public:
      /** Initialize your data structure here. */
      Trie() {
          root = new TrieNode();
      }
      
      /** Inserts a word into the trie. */
      void insert(string word) {
          TrieNode *p = root;
          for (auto & iter : word) {
              int i = iter - 'a';
              if (!p->child[i]) {
                  p->child[i] = new TrieNode();
                  p = p->child[i];
              } else {
                  p = p->child[i];
              }
          }
          p->isWord = true;
      }
      
      /** Returns if the word is in the trie. */
      bool search(string word) {
          TrieNode *p = root;
          for (auto & iter : word) {
              int i = iter - 'a';
              if (p->child[i]) {
                  p = p->child[i];
              } else {
                  return false;
              }
          }
          return (p->isWord);
      }
      
      /** Returns if there is any word in the trie that starts with the given prefix. */
      bool startsWith(string prefix) {
           TrieNode *p = root;
           for (auto & iter : prefix) {
              int i = iter - 'a';
              if (p->child[i]) {
                  p = p->child[i];
              } else {
                  return false;
              }
          }
          return true;
      }
  private:
      TrieNode* root;
  };
  
  
  /**
   * Your Trie object will be instantiated and called as such:
   * Trie* obj = new Trie();
   * obj->insert(word);
   * bool param_2 = obj->search(word);
   * bool param_3 = obj->startsWith(prefix);
   */