Trie

参考

https://en.wikipedia.org/wiki/Trie

a trie, also called digital tree or prefix tree, is a kind of search tree—an ordered tree data structure used to store a dynamic set or associative array where the keys are usually strings

也叫前缀树， 特定情况下替代set 和map。这时候key是字符串。

LeetCode：208. Implement Trie (Prefix Tree)
LeetCode：211. Add and Search Word - Data structure design
LeetCode：212. Word Search II

下面我们就一步步来实现Trie，并做题

一、初步实现Trie树结构

208. Implement Trie (Prefix Tree)

https://leetcode.com/problems/implement-trie-prefix-tree/description/

#include<cstdio>

#include<iostream>

#include<string>

#include<vector>

#include<algorithm>

using namespace std;

/**

* 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);

*/

const int letter_size=26;//字符集大小

struct TrieNode

{

TrieNode* children[letter_size]={0};

bool isWord = false;

TrieNode(){

}

~TrieNode(){

for(int i=0; i<letter_size; i++) if(children[i]) delete children[i];

}

};

struct Trie {

TrieNode* root;

/** Initialize your data structure here. */

Trie() {

root=new TrieNode();

}

~Trie(){

delete root;

}

int idx(char c)

{

return c - 'a';

}

/** Inserts a word into the trie. */

void insert(string word) {

TrieNode*p = root;

int len = word.length();

for(int i=0; i < len; i++){

int c = idx(word[i]);

if(!p->children[c])

p->children[c] = new TrieNode();

p = p->children[c];

}

p->isWord = true;

}

/** Returns if the word is in the trie. */

bool search(string word) {

TrieNode *p=root;

int len = word.length();

for(int i=0; i < len; i++){

p = p->children[idx(word[i])];

if(!p)

return false;

}

return p->isWord;

}

/** Returns if there is any word in the trie that starts with the given prefix. */

bool startsWith(string word) {

TrieNode *p=root;

int len = word.length();

for(int i=0; i < len; i++){

p = p->children[idx(word[i])];

if(!p)

return false;

}

return true;

}

};

int main()

{

Trie trie;

trie.insert("apple");

cout<< trie.search("apple") << endl;   // returns true

cout<< trie.search("app") << endl;     // returns false

cout<< trie.startsWith("app") << endl; // returns true

trie.insert("app");

cout<< trie.search("app") << endl;;     // returns true

return 0;

}

来源：oschina

链接：https://my.oschina.net/u/4305000/blog/4305276