字典树（前缀数）例题以及模板

字典树（前缀数）例题以及模板

先放题目

1. leetcode 208 -基础字典树
   https://leetcode.com/problems/implement-trie-prefix-tree/
2. leetcode 211-字典树模糊匹配
   https://leetcode.com/problems/add-and-search-word-data-structure-design/description/
3. leetcode 212-二维数值字典树(bfs)
   https://leetcode.com/problems/word-search-ii/description/

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解析

网上字典树的原理和解析很多，就不做太多分析和讲解了，直接上题简易模板。题型变化基于模板修改就可以。

1. 字典树的结构

class TrieNode {
    public char val;
    public boolean isWord; 
    public TrieNode[] children = new TrieNode[26];
    public TrieNode() {}
    TrieNode(char c){
        TrieNode node = new TrieNode();
        node.val = c;
    }
}

• 添加 insert(aabccc)

  public void insert(String word) {
        TrieNode ws = root;
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(ws.children[c - 'a'] == null){
                ws.children[c - 'a'] = new TrieNode(c);
            }
            ws = ws.children[c - 'a'];
        }
        ws.isWord = true;
    }

• 全匹配搜索 search(aabccc)->true

 public boolean search(String word) {
        TrieNode ws = root; 
        for(int i = 0; i < word.length(); i++){
            char c = word.charAt(i);
            if(ws.children[c - 'a'] == null) return false;
            ws = ws.children[c - 'a'];
        }
        return ws.isWord;
    }

• 前缀搜索 startsWith(aabc)->true

 public boolean startsWith(String prefix) {
        TrieNode ws = root; 
        for(int i = 0; i < prefix.length(); i++){
            char c = prefix.charAt(i);
            if(ws.children[c - 'a'] == null) return false;
            ws = ws.children[c - 'a'];
        }
        return true;
    }

• 模糊匹配 fuzzySearch(.abc..)->true

  public boolean fuzzySearch(String word) {
      return search(word.toCharArray(), 0, root);                  
  }
  
  private boolean fuzzySearch(char[] chars, int index, TrieNode parent){
      if (index == chars.length){
          if (parent.isLeaf){
              return true;
          }
          return false;
      }
      TrieNode [] childNodes = parent.children;
      char c = chars[index];
      if (c == '.'){
          for (int i=0;iif (n !=null){
                  boolean b = fuzzySearch(chars, index+1, n);
                  if (b){
                      return true;
                  }
              }
          }
          return false;
      }
      TrieNode node = childNodes[c-'a'];
      if (node == null){
          return false;
      }
      return search(chars, ++index, node);
  }