力扣labuladong——一刷day91

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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;
        }
    }
}