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前言

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Trie 树又叫字典树、前缀树、单词查找树，是一种二叉树衍生出来的高级数据结构，主要应用场景是处理字符串前缀相关的操作

一、力扣208. 实现 Trie (前缀树)

class Trie {private int size;private static final int R = 58;private TrieNode root = null;static class TrieNode{String val;TrieNode[] chialdren = new TrieNode[R];}public Trie() {this.size = 0;}public void insert(String word) {this.root = put(root,0,word);}public boolean search(String word) {return get(word,0,root);}public boolean startsWith(String prefix) {return getPrefix(prefix,0,root);}public TrieNode put(TrieNode node,int index,String word){if(node == null){node = new TrieNode();}if(index == word.length()){node.val = word;return node;}char c = word.charAt(index);node.chialdren[c-'A'] = put(node.chialdren[c-'A'],index+1,word);return node;}public boolean get(String word,int index,TrieNode node){if(node == null){return false;}if(index == word.length()){if(node.val != null){return true;}else{return false;}}char c = word.charAt(index);if(get(word,index+1,node.chialdren[c-'A'])){return true;}return false;}public boolean getPrefix(String word,int index,TrieNode node){if(node == null){return false;}if(index == word.length()){return true;}char c = word.charAt(index);if(getPrefix(word,index+1,node.chialdren[c-'A'])){return true;}return false;}
}/*** 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);*/

二、力扣648. 单词替换

class Solution {public String replaceWords(List<String> dictionary, String sentence) {Trie trie = new Trie();for(int i = 0; i < dictionary.size(); i ++){trie.put(dictionary.get(i));}StringBuilder sb = new StringBuilder(sentence);StringBuilder res = new StringBuilder();for(int i = 0, j = 0; j <= sentence.length(); j++) { if(j < sentence.length() && sb.charAt(j) != ' '){continue;} else {String cur = trie.get(sb.substring(i, j));res.append(cur);if (j < sentence.length()) {res.append(" ");}i = j + 1;}}return res.toString();}class Trie{static final int R = 26;TrieNote root = null;static class TrieNote{String val;TrieNote[] children = new TrieNote[R];}String get(String dic){int len = Integer.MAX_VALUE;return getOne(dic, root, 0, len);}String getOne(String dic, TrieNote node, int index, int len){if(node == null || index == dic.length()){return len == Integer.MAX_VALUE ? dic : dic.substring(0,len-1);}if(node.val != null){len = Math.min(len,index+1);}char c = dic.charAt(index);return getOne(dic, node.children[c-'a'],index+1,len);}void put(String dic){this.root = putA(root,0,dic);}TrieNote putA(TrieNote node, int index, String dic){if(node == null){node = new TrieNote();}if(index == dic.length()){node.val = dic;return node;}char c = dic.charAt(index);node.children[c-'a'] = putA(node.children[c-'a'],index+1,dic);return node;}}
}