Implement Trie (Prefix Tree)
Tags: leetcode, dsa, theabbie
Published: 2022-06-14 00:30:40

A [**trie**](https://en.wikipedia.org/wiki/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`.

**SOLUTION:**

    class Node:
        def __init__(self, val=None, children=[], end=False):
            self.val = val
            self.children = children
            self.end = end
    
    class Trie:
        def __init__(self):
            self.root = Node(val=None, children=[])
    
        def insert(self, word: str) -> None:
            n = len(word)
            curr = self.root
            for i, c in enumerate(word):
                found = False
                for node in curr.children:
                    if node.val == c:
                        curr = node
                        found = True
                        break
                if not found:
                    newcurr = Node(val=c, children=[])
                    curr.children.append(newcurr)
                    curr = newcurr
            curr.end = True
    
        def search(self, word: str) -> bool:
            n = len(word)
            curr = self.root
            for i, c in enumerate(word):
                found = False
                for node in curr.children:
                    if node.val == c:
                        curr = node
                        found = True
                        break
                if not found:
                    return False
            return curr.end
    
        def startsWith(self, prefix: str) -> bool:
            n = len(prefix)
            curr = self.root
            for i, c in enumerate(prefix):
                found = False
                for node in curr.children:
                    if node.val == c:
                        curr = node
                        found = True
                        break
                if not found:
                    return False
            return True
    
    # class Trie:
    
    #     def __init__(self):
    #         self.trie = {}
    
    #     def insert(self, word: str) -> None:
    #         word = list(word) + [-1]
    #         n = len(word)
    #         for i in range(n - 1):
    #             if i not in self.trie:
    #                 self.trie[i] = {}
    #             if word[i] in self.trie[i]:
    #                 self.trie[i][word[i]].add(word[i + 1])
    #             else:
    #                 self.trie[i][word[i]] = {word[i + 1]}
    
    #     def search(self, word: str, isPartial = False) -> bool:
    #         if not isPartial:
    #             word = list(word) + [-1]
    #         n = len(word)
    #         if n == 1:
    #             if word[0] in self.trie.get(0, {}):
    #                 return True
    #             else:
    #                 return False
    #         for i in range(n - 1):
    #             if i not in self.trie or word[i] not in self.trie[i] or word[i + 1] not in self.trie[i][word[i]]:
    #                 return False
    #         return True
    
    #     def startsWith(self, prefix: str) -> bool:
    #         return self.search(prefix, isPartial = True)
    
    
    # Your Trie object will be instantiated and called as such:
    # obj = Trie()
    # obj.insert(word)
    # param_2 = obj.search(word)
    # param_3 = obj.startsWith(prefix)