Trie树
字典树,即Trie树,又称单词查找树或键树,是一种树形结构。典型应用是用于统计和排序大量的字符串(但不仅限于字符串),所以经常被搜索引擎系统用于文本词频统计。它的优点是:最大限度地减少无谓的字符串比较,查询效率比哈希表高。
//leetcode submit region begin(Prohibit modification and deletion) class Trie { TrieNode root; /** Initialize your data structure here. */ public Trie() { root = new TrieNode(); } /** Inserts a word into the trie. */ public void insert(String word) { TrieNode cur =root; char c; for(int i = 0;i<word.length();i++){ c =word.charAt(i); if(cur.get(c)!=null){ cur= cur.get(c); }else { cur.put(c,new TrieNode()); cur= cur.get(c); } } cur.setEnd(); } /** Returns if the word is in the trie. */ public boolean search(String word) { TrieNode cur = root; char c; for(int i=0;i<word.length();i++){ c = word.charAt(i); if(cur.get(c)==null) return false; cur=cur.get(c); } return cur.isEnd==true?true:false; } /** Returns if there is any word in the trie that starts with the given prefix. */ public boolean startsWith(String prefix) { TrieNode cur = root; char c; for(int i=0;i<prefix.length();i++){ c = prefix.charAt(i); if(cur.get(c)==null) return false; cur=cur.get(c); } return true; } } class TrieNode{ Map <Character, TrieNode> nextTreeNode; boolean isEnd; public TrieNode(){ nextTreeNode = new HashMap<>(); isEnd = false; } public boolean containsKey(char c){ return nextTreeNode.containsKey(c); } public TrieNode get(char c){ return nextTreeNode.get(c); } public void put(char c,TrieNode node){ nextTreeNode.put(c,node); } public boolean isEnd(){ return isEnd; } public void setEnd(){ isEnd = true; } }
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