Trie.cpp

#include<bits/stdc++.h>
using namespace std;

class TrieNode{
public:
    TrieNode* next[26];
    bool isword;
    TrieNode() {
        memset(next, NULL, sizeof(next));
        isword = false;
    }
    ~TrieNode() {
        for (int i = 0; i < 26; ++i)
            if (next[i]) delete next[i];
    }
};


class Trie {
    TrieNode* root;
public:
    /** Initialize your data structure here. */
    Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    void insert(string word) {
        TrieNode* p = root;
        int n = word.size();
        for (int i = 0; i < n; ++i) {
            int idx = word[i] - 'a';
            if (!p->next[idx]) {
                p->next[idx] = new TrieNode();
            }
            p = p->next[idx];
        }
        p->isword = true;
    }
    
    /** Returns if the word is in the trie. */
    bool search(string word) {
        TrieNode* p = root;
        int n = word.size();
        for (int i = 0; i < n && p; ++i) {
            p = p->next[word[i]-'a'];
        }
        return p && p->isword;

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

    ~Trie() {
        delete 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);
 */