Implement Trie (Prefix Tree) -- leetcode

标签：leetcode   字典树   

Implement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

基本思路，

作一个26叉树。

本来想作一个27叉，用额外一叉，表示字符串的结束字符(‘\0‘). 但感觉此法浪费内存。后增加一个标志isword，来表示第27叉。

根结点，不表示任何字符。

当前节点所代表的字符位于父结点的分叉中。

class TrieNode {
public:
    // Initialize your data structure here.
    TrieNode() : childs(26), isword(false) {
        
    }
    
    TrieNode *get(char ch, bool create = false) {
        const int index = ch - 'a';
        if (create && !childs[index]) {
            childs[index] = new TrieNode();
        }
        return childs[index]; 
    }
    
    bool isword;
private:
    vector<TrieNode *> childs;
};

class Trie {
public:
    Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    void insert(string word) {
        auto t = root;
        for (auto ch: word) {
            t = t->get(ch, true);
        }
        t->isword = true;
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        auto t = find(word);
        return t && t->isword;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix) {
        return !!find(prefix);
    }

private:
    TrieNode *find(string word) {
        auto t = root;
        for (auto ch: word) {
            if (!(t = t->get(ch)))
                break;
        }
        return t;
    }

    TrieNode* root;
};

// Your Trie object will be instantiated and called as such:
// Trie trie;
// trie.insert("somestring");
// trie.search("key");

Implement Trie (Prefix Tree) -- leetcode

标签：leetcode   字典树   

原文地址：http://blog.csdn.net/elton_xiao/article/details/47209923