Hard 211题 Add and Search Word - Data structure design

Question:

Design a data structure that supports the following two operations:

void addWord(word)bool search(word)

search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.

For example:

addWord("bad")addWord("dad")addWord("mad")search("pad") -> falsesearch("bad") -> truesearch(".ad") -> truesearch("b..") -> true

Solution: 思路其实很清晰，看了discussion后，但还是搞了很久TAT

public class WordDictionary {    TrieNode root=new TrieNode();    private class TrieNode{        // Initialize your data structure here.        boolean isLeaf;        TrieNode[] children = new TrieNode[26];            }        // Adds a word into the data structure.    public void addWord(String word) {        addWord(word.toCharArray(), 0,root);    }        public void addWord(char[] chars, int index,TrieNode parent){        char c=chars[index];        TrieNode node = parent.children[c-'a'];        if(node==null){            node=new TrieNode();            parent.children[c-'a']=node;        }        if(index==chars.length-1)        {            node.isLeaf=true;            return;        }        addWord(chars,++index,node);    }    // 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(word.toCharArray(),0,root);    }        private boolean search(char[] chars, int index, TrieNode parent){        if(index==chars.length) //why????        {            if(parent.isLeaf==true)                return true;            return false;        }        char c=chars[index];        TrieNode[] node=parent.children;        if(c=='.')        {            for(int i=0;i<=node.length-1;i++)            {                if(node[i]!=null)                {                    if(search(chars,index+1,node[i]))                        return true;                }            }            return false;        }        TrieNode nextnode=node[c-'a'];        if(nextnode==null)            return false;                return search(chars,++index,nextnode);    }}// Your WordDictionary object will be instantiated and called as such:// WordDictionary wordDictionary = new WordDictionary();// wordDictionary.addWord("word");// wordDictionary.search("pattern");