LeetCode in Python

211. Design Add and Search Words Data Structure

Medium

Design a data structure that supports adding new words and finding if a string matches any previously added string.

Implement the WordDictionary class:

• WordDictionary() Initializes the object.
• void addWord(word) Adds word to the data structure, it can be matched later.
• bool search(word) Returns true if there is any string in the data structure that matches word or false otherwise. word may contain dots '.' where dots can be matched with any letter.

Example:

Input

["WordDictionary","addWord","addWord","addWord","search","search","search","search"] [[],["bad"],["dad"],["mad"],["pad"],["bad"],[".ad"],["b.."]]

Output

[null,null,null,null,false,true,true,true]

Explanation

WordDictionary wordDictionary = new WordDictionary();
wordDictionary.addWord("bad");
wordDictionary.addWord("dad");
wordDictionary.addWord("mad");
wordDictionary.search("pad"); // return False
wordDictionary.search("bad"); // return True
wordDictionary.search(".ad"); // return True
wordDictionary.search("b.."); // return True 

Constraints:

• 1 <= word.length <= 500
• word in addWord consists lower-case English letters.
• word in search consist of '.' or lower-case English letters.
• At most 50000 calls will be made to addWord and search.

Solution

class TrieNode:
    def __init__(self):
        self.children = {}    # char -> TrieNode
        self.is_end = False   # end of word

class WordDictionary:
    def __init__(self):
        self.root = TrieNode()

    # Word insert karna
    def addWord(self, word: str) -> None:
        node = self.root
        for ch in word:
            if ch not in node.children:
                node.children[ch] = TrieNode()
            node = node.children[ch]
        node.is_end = True

    # Word search karna
    def search(self, word: str) -> bool:
        def dfs(node, i):
            # Base case: agar pura word traverse ho gaya
            if i == len(word):
                return node.is_end

            ch = word[i]

            # Case 1: agar char "." hai → sab children explore karo
            if ch == ".":
                for child in node.children.values():
                    if dfs(child, i + 1):
                        return True
                return False

            # Case 2: normal character
            else:
                if ch not in node.children:
                    return False
                return dfs(node.children[ch], i + 1)

        return dfs(self.root, 0)


# Your WordDictionary object will be instantiated and called as such:
# obj = WordDictionary()
# obj.addWord(word)
# param_2 = obj.search(word)

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