208. 实现 Trie (前缀树)
字典树
转自评论中某大佬，加入了一个preorder可以查看一下树的构造是不是对的
注意：
search和startsWith只差了最后一句return。因为
insert的时候插入的是word，最后一个字符结点会保留isWord=true，但是中间的就不一定了，所以startsWith直接返回true，search返回t->isWord
#include <iostream>
#include <string>
#include <vector>
using namespace std;
class Trie {
Trie *child[26];
bool isWord;
public:
/** Initialize your data structure here. */
Trie() {
isWord = false;
for (int i = 0; i < 26; i++) {
child[i] = nullptr;
}
}
void preorder(Trie *node) {
if (node == nullptr)
return;
for (int i = 0; i < 26; i++) {
if (node->child[i] != nullptr) {
cout << char(i + 'a') << " ";
preorder(node->child[i]);
}
}
}
/** Inserts a word into the trie. */
void insert(string word) {
Trie *t = this;
for (char c : word) {
if (!t->child[c - 'a']) {
t->child[c - 'a'] = new Trie();
}
t = t->child[c - 'a'];
}
t->isWord = true;
}
/** Returns if the word is in the trie. */
bool search(string word) {
Trie *t = this;
for (char c : word) {
if (!t->child[c - 'a']) {
return false;
}
t = t->child[c - 'a'];
}
return t->isWord;
}
/** Returns if there is any word in the trie that starts with the given
* prefix. */
bool startsWith(string prefix) {
Trie *t = this;
for (char c : prefix) {
if (!t->child[c - 'a']) {
return false;
}
t = t->child[c - 'a'];
}
return true;
}
};
/**
* 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);
*/
int main() {
Trie s;
s.insert(string("asdf"));
s.insert(string("aszx"));
s.insert(string("abss"));
s.preorder(&s);
return 0;
}
