package com.odyssey.app.algorithm.lc.trie;
/**
* @author Dingsheng Huang
* @date 2020/3/12 23:45
*
* 208
* medium
* https://leetcode.com/problems/implement-trie-prefix-tree/
*
* Implement a trie with insert, search, and startsWith methods.
*
* Example:
*
* Trie trie = new Trie();
*
* trie.insert("apple");
* trie.search("apple"); // returns true
* trie.search("app"); // returns false
* trie.startsWith("app"); // returns true
* trie.insert("app");
* trie.search("app"); // returns true
* Note:
*
* You may assume that all inputs are consist of lowercase letters a-z.
* All inputs are guaranteed to be non-empty strings.
*
*/
public class ImplementTrie {
class Trie {
String word = "";
Trie[] children = new Trie[26];
/** Initialize your data structure here. */
public Trie() {
}
/** Inserts a word into the trie. */
public void insert(String word) {
Trie currNode = this;
char[] chs = word.toCharArray();
for (int i = 0; i < chs.length; i++) {
int idx = chs[i] - 'a';
if (currNode.children[idx] == null) {
currNode.children[idx] = new Trie();
}
currNode = currNode.children[idx];
}
currNode.word = word;
}
private boolean searchRes;
/** Returns if the word is in the trie. */
public boolean search(String word) {
searchRes = false;
dfs(this, word.toCharArray(), 0);
return searchRes;
}
private boolean prefixRes;
/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String prefix) {
prefixRes = false;
dfs2(this, prefix.toCharArray(), 0);
return prefixRes;
}
private void dfs(Trie root, char[] chs, int idx) {
if (root == null || idx == chs.length) {
return;
}
if (root.children[chs[idx] - 'a'] != null) {
// access the border
if (idx == chs.length - 1) {
if (root.children[chs[idx] - 'a'].word.length() > 0) {
searchRes = true;
}
}
// next
dfs(root.children[chs[idx] - 'a'], chs, idx + 1);
}
}
private void dfs2(Trie root, char[] chs, int idx) {
if (root == null || idx == chs.length) {
return;
}
if (root.children[chs[idx] - 'a'] != null) {
// access the border
if (idx == chs.length - 1) {
prefixRes = true;
}
// next
dfs(root.children[chs[idx] - 'a'], chs, idx + 1);
}
}
}
/**
* Your Trie object will be instantiated and called as such:
* Trie obj = new Trie();
* obj.insert(word);
* boolean param_2 = obj.search(word);
* boolean param_3 = obj.startsWith(prefix);
*/
}
