Prefix and Suffix Search

Given many words, words[i] has weight i.

Design a class WordFilter that supports one function, WordFilter.f(String prefix, String suffix). It will return the word with given prefix and suffix with maximum weight. If no word exists, return -1.

Examples:

Input:
WordFilter(["apple"])
WordFilter.f("a", "e") // returns 0
WordFilter.f("b", "") // returns -1

分析：因为要找出word一定begin with prefix，以及end with suffix，有点麻烦。其实找begin with prefix不麻烦，麻烦的是怎么找end with suffix. 这里有点巧的方法是对于每个word，把它所有的
suffx_word放在trie里，比如apple, 我们就把 "_apple", "e_apple", "le_apple", "ple_apple", "pple_apple", "apple_apple" 都存在trie里。这样可以用trie把所有的情况都包括了。

 class TrieNode {
     char ch;
     int weight;
     Map<Character, TrieNode> map;

     public TrieNode(char ch, int weight) {
         this.ch = ch;
         this.weight = weight;
         map = new HashMap<>();
     }

     public TrieNode getChildNode(char ch) {
         return map.get(ch);
     }
 }

 public class WordFilter {
     private TrieNode root = new TrieNode(' ', -);
     public WordFilter(String[] words) {
         for (int weight = ; weight < words.length; weight++) {
             List<String> suffixList = generateSuffixList(words[weight]);
             for (String word : suffixList) {
                 addWord(word, weight);
             }
         }
     }

     public void addWord(String word, int weight) {
         TrieNode current = root;
         for (int i = ; i < word.length(); i++) {
             char ch = word.charAt(i);
             TrieNode node = current.getChildNode(ch);
             if (node == null) {
                 current.map.put(ch, new TrieNode(ch, weight));
                 node = current.getChildNode(ch);
             }
             node.weight = Math.max(weight, node.weight);
             current = node;
         }
     }
     private List<String> generateSuffixList(String word) {
         List<String> suffixList = new ArrayList<>();
         int length = word.length();
         for (int i = length; i >= ; i--) {
             String sub = word.substring(i, length);
             suffixList.add(sub + "_" + word);
         }
         return suffixList;
     }

     public int f(String prefix, String suffix) {
         if (root == null) return -;
         TrieNode current = root;

         String word = suffix + "_" + prefix;
         for (char ch : word.toCharArray()) {
             current = current.getChildNode(ch);
             if (current == null) {
                 return -;
             }
         }
         return current.weight;
     }
 }