【LeetCode】208. Implement Trie (Prefix Tree)

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

.

一个字母代表一个子树，因此为26叉树，end标记表示是否存在以该字母为结尾的字符串。

class TrieNode {
public:
TrieNode* children[26];
bool end;
// Initialize your data structure here.
TrieNode() {
for(int i = 0; i < 26; i ++)
children[i] = NULL;
end = false;
}
};

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

// Inserts a word into the trie.
void insert(string word) {
int i = 0;
TrieNode* curNode = root;
while(i < word.size() && curNode->children[word[i]-'a'] != NULL)
{
curNode = curNode->children[word[i]-'a'];
i ++;
}
if(i == word.size())
{
if(curNode->end == true)
// exist
return;
else
// insert
curNode->end = true;
}
else
{
while(i < word.size())
{
curNode->children[word[i]-'a'] = new TrieNode();
curNode = curNode->children[word[i]-'a'];
i ++;
}
curNode->end = true;
}
}

// Returns if the word is in the trie.
bool search(string word) {
int i = 0;
TrieNode* curNode = root;
while(i < word.size() && curNode->children[word[i]-'a'] != NULL)
{
curNode = curNode->children[word[i]-'a'];
i ++;
}
if(i == word.size() && curNode->end == true)
// curNode must be leaf
return true;
else
return false;
}

// Returns if there is any word in the trie
// that starts with the given prefix.
bool startsWith(string prefix) {
int i = 0;
TrieNode* curNode = root;
while(i < prefix.size() && curNode->children[prefix[i]-'a'] != NULL)
{
curNode = curNode->children[prefix[i]-'a'];
i ++;
}
if(i == prefix.size())
// curNode might be left or not
return true;
else
return false;
}

private:
TrieNode* root;
};

// Your Trie object will be instantiated and called as such:
// Trie trie;
// trie.insert("somestring");
// trie.search("key");