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") -> false
search("bad") -> true
search(".ad") -> true
search("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");