745. Prefix and Suffix Search

Problem Link

Description

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Design a special dictionary that searches the words in it by a prefix and a suffix.

Implement the WordFilter class:

• WordFilter(string[] words) Initializes the object with the words in the dictionary.
• f(string pref, string suff) Returns the index of the word in the dictionary, which has the prefix pref and the suffix suff. If there is more than one valid index, return the largest of them. If there is no such word in the dictionary, return -1.

 

Example 1:

Input
["WordFilter", "f"]
[[["apple"]], ["a", "e"]]
Output
[null, 0]
Explanation
WordFilter wordFilter = new WordFilter(["apple"]);
wordFilter.f("a", "e"); // return 0, because the word at index 0 has prefix = "a" and suffix = "e".

 

Constraints:

• 1 <= words.length <= 104
• 1 <= words[i].length <= 7
• 1 <= pref.length, suff.length <= 7
• words[i], pref and suff consist of lowercase English letters only.
• At most 104 calls will be made to the function f.

Solution

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Python3

class WordFilter:
 
    def __init__(self, words: List[str]):
        self.mp = collections.defaultdict(int)
        self.prefixes = collections.defaultdict(set)
        self.suffixes = collections.defaultdict(set)
        
        for index,word in enumerate(words):
            prefix = ""
            suffix = ""
            
            for char in [""] + list(word):
                prefix += char
                self.prefixes[prefix].add(word)
            
            for char in [""] + list(word[::-1]):
                suffix += char
                self.suffixes[suffix[::-1]].add(word)
            
            self.mp[word] = index
 
    def f(self, prefix: str, suffix: str) -> int:
        res = -1
        
        for word in self.prefixes[prefix] & self.suffixes[suffix]:
            res = max(res, self.mp[word])
        
        return res
 
 
# Your WordFilter object will be instantiated and called as such:
# obj = WordFilter(words)
# param_1 = obj.f(prefix,suffix)