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);
 */