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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211. 添加与搜索单词 - 数据结构设计

class WordDictionary {static final int R = 26;TrieNode root = null;static class TrieNode{String val;TrieNode[] children = new TrieNode[R];}public WordDictionary() {}public void addWord(String word) {root = put(root,word,0);}public boolean search(String word) {return get(root,word,0);}boolean get(TrieNode node, String word, int index){if(node == null){return false;}if(index == word.length()){if(node.val != null){return true;}return false;}char c = word.charAt(index);if(c == '.'){for(int i = 0; i < R; i ++){if(get(node.children[i],word,index+1)){return true;}}}else{if(get(node.children[c-'a'],word,index+1)){return true;}}return false;}TrieNode put(TrieNode node, String word, int index){if(node == null){node = new TrieNode();}if(index == word.length()){node.val = word;return node;}char c = word.charAt(index);node.children[c-'a'] = put(node.children[c-'a'],word,index+1);return node;}
}/*** Your WordDictionary object will be instantiated and called as such:* WordDictionary obj = new WordDictionary();* obj.addWord(word);* boolean param_2 = obj.search(word);*/

二、力扣677. 键值映射

class MapSum {static final int R = 26;TrieNode root = null;int sum = 0;static class TrieNode{int val = 0;TrieNode[] children = new TrieNode[R];}public MapSum() {}public void insert(String key, int val) {root = put(root,key,0,val);}public int sum(String prefix) {get(root,prefix,0);int temp = sum;sum = 0;return temp;}void get(TrieNode node, String prefix, int index){if(node == null){return;}if(index < prefix.length()){char c = prefix.charAt(index);// sum += node.val;get(node.children[c-'a'],prefix,index+1);}else{sum += node.val;for(int i = 0; i < R; i ++){if(node.children[i] != null){get(node.children[i],prefix,index+1);}}}}TrieNode put(TrieNode node, String key, int index,int val){if(node == null){node = new TrieNode();}if(index == key.length()){node.val = val;return node;}char c = key.charAt(index);node.children[c-'a'] = put(node.children[c-'a'],key,index+1,val);return node;}
}/*** Your MapSum object will be instantiated and called as such:* MapSum obj = new MapSum();* obj.insert(key,val);* int param_2 = obj.sum(prefix);*/