LeetCode-208 Implement Trie (Prefix Tree)

题目描述

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

题目大意

实现对一棵树的插入、搜索以及前序查找操作。

（树的每个节点代表一个小写字母，从根节点到叶节点代表一个完整的单词）

示例

Trie trie = new Trie();trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

解题思路

感谢Leetcode@cxq1992提供的思路，采用较为工程化的方法完成树结点的记录保存与操作。

复杂度分析

时间复杂度：O(NULL)

空间复杂度：O(NULL)

代码

class node {
public:node() : val(' '), end(false), shared(0) {}node(char c) : val(c), end(false), shared(0) {}node* subchild(char c) {if(!child.empty()) {for(auto chi : child) {if(chi->val == c)return chi;}}return NULL;}~node() {for(auto chi : child)delete chi;}//该树结点所保存的小写字母char val;//该结点是否是叶节点bool end;//子节点的个数int shared;//子节点保存vector<node*> child;
};class Trie {
public:/** Initialize your data structure here. */Trie() {root = new node();}/** Inserts a word into the trie. */void insert(string word) {if(search(word))return;node* cur = root;for(char c : word) {node* tmp = cur->subchild(c);if(tmp == NULL) {tmp = new node(c);cur->child.push_back(tmp);cur = tmp;}else {cur = tmp;}++cur->shared;}cur->end = true;}/** Returns if the word is in the trie. */bool search(string word) {node* tmp = root;for(char c : word) {tmp = tmp->subchild(c);if(tmp == NULL)return false;}return tmp->end;}/** Returns if there is any word in the trie that starts with the given prefix. */bool startsWith(string prefix) {node* tmp = root;for(char c : prefix) {tmp = tmp->subchild(c);if(tmp == NULL)return false;}return true;}private:node* root;
};/*** Your Trie object will be instantiated and called as such:* Trie* obj = new Trie();* obj->insert(word);* bool param_2 = obj->search(word);* bool param_3 = obj->startsWith(prefix);*/