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(' ', -1);
    public WordFilter(String[] words) {
        for (int weight = 0; 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 = 0; 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 >= 0; i--) {
            String sub = word.substring(i, length);
            suffixList.add(sub + "_" + word);
        }
        return suffixList;
    }
    
    
    public int f(String prefix, String suffix) {
        if (root == null) return -1;
        TrieNode current = root;
        
        String word = suffix + "_" + prefix;
        for (char ch : word.toCharArray()) {
            current = current.getChildNode(ch);
            if (current == null) {
                return -1;
            }
        }
        return current.weight;
    }
}