Prefix and Suffix Search

Design a special dictionary which has some words and allows you to search 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 prefix, string suffix)` Returns the index of the word in the dictionary which has the prefix `prefix` and the suffix `suffix`. 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 <= 15000` `1 <= words[i].length <= 10` `1 <= prefix.length, suffix.length <= 10` `words[i]`, `prefix` and `suffix` consist of lower-case English letters only. At most `15000` calls will be made to the function `f`.