208. Implement Trie (Prefix Tree)

Easy
​
A trie (pronounced as "try") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.
Implement the Trie class:
  • Trie() Initializes the trie object.
  • void insert(String word) Inserts the string word into the trie.
  • boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.
  • boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.
Example 1:
Input
["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
Output
[null, null, true, false, true, null, true]
Explanation
Trie trie = new Trie();
trie.insert("apple");
trie.search("apple"); // return True
trie.search("app"); // return False
trie.startsWith("app"); // return True
trie.insert("app");
trie.search("app"); // return True
Constraints:
  • 1 <= word.length, prefix.length <= 2000
  • word and prefix consist only of lowercase English letters.
  • At most 3 * 104 calls in total will be made to insert, search, and startsWith.

解題

這題要打造一個 Prefix Trie
type Trie struct {
children [26]*Trie
isTerminal bool
}
​
​
func Constructor() Trie {
return Trie{}
}
​
​
func (this *Trie) Insert(word string) {
for i:=0; i<len(word); i++ {
if this.children[word[i]-'a'] == nil {
this.children[word[i]-'a'] = &Trie{}
}
this = this.children[word[i]-'a']
}
this.isTerminal = true
}
​
​
func (this *Trie) Search(word string) bool {
for i:=0; i<len(word); i++ {
if this.children[word[i]-'a'] == nil {
return false
}
this = this.children[word[i]-'a']
}
if this.isTerminal == false {
return false
}
​
return true
}
​
​
func (this *Trie) StartsWith(prefix string) bool {
for i:=0; i<len(prefix); i++ {
if this.children[prefix[i]-'a'] == nil {
return false
}
this = this.children[prefix[i]-'a']
}
​
return true
}
​
​
/**
* Your Trie object will be instantiated and called as such:
* obj := Constructor();
* obj.Insert(word);
* param_2 := obj.Search(word);
* param_3 := obj.StartsWith(prefix);
*/