leetcode 添加與搜索單詞 - 數據結構設計

用單詞查找樹，實現方法有很多，但是看了算法第4版的實現發現代碼真的簡潔強大。

可以先看這篇文章：單詞查找樹

這裏搜索單詞只需要判斷true或false，不需要全部匹配，稍稍修改了下。

class WordDictionary {

        private Node root;
        private static int R = 26;

        static class Node {
            private boolean isWordEnd = false;
            private Node[] next = new Node[R];
        }

        /**
         * Initialize your data structure here.
         */
        public WordDictionary() {
        }

        /**
         * Adds a word into the data structure.
         */
        public void addWord(String word) {
            root = put(root, word, 0);
        }

        private Node put(Node x, String word, int d) {
            if (x == null) {
                x = new Node();
            }
            if (d == word.length()) {
                x.isWordEnd = true;
                return x;
            }
            char c = word.charAt(d);
            x.next[c - 'a'] = put(x.next[c - 'a'], word, d + 1);
            return x;
        }

        /**
         * Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter.
         */
        public boolean search(String word) {
            return search(root, word, 0);
        }

        private boolean search(Node x, String pat, int d) {
            if (x == null) {
                return false;
            }
            if (d == pat.length()) {
                return x.isWordEnd;
            }
            char c = pat.charAt(d);
            if (c == '.') {
                // 搜索所有節點
                for (int i = 0; i < R; i++) {
                    if (search(x.next[i], pat, d + 1)) {
                        return true;
                    }
                }
            } else {
                return search(x.next[c - 'a'], pat, d + 1);
            }
            return false;
        }
}