单词频率
- 难度:Medium
- 题目链接:https://leetcode-cn.com/problems/words-frequency-lcci/
题目描述
设计一个方法,找出任意指定单词在一本书中的出现频率。
你的实现应该支持如下操作:
WordsFrequency(book)
构造函数,参数为字符串数组构成的一本书get(word)
查询指定单词在书中出现的频率
示例:
WordsFrequency wordsFrequency = new WordsFrequency({"i", "have", "an", "apple", "he", "have", "a", "pen"}); wordsFrequency.get("you"); //返回0,"you"没有出现过 wordsFrequency.get("have"); //返回2,"have"出现2次 wordsFrequency.get("an"); //返回1 wordsFrequency.get("apple"); //返回1 wordsFrequency.get("pen"); //返回1
提示:
book[i]
中只包含小写字母1 <= book.length <= 100000
1 <= book[i].length <= 10
get
函数的调用次数不会超过100000
解法:
可以使用一个 map 统计词频,也可以使用一个 trie 来存储所有的单词,并统计词频。
struct Node{
Node():count(0){}
int count;
Node* children[26]{};
};
class Trie{
private:
public:
void insert(const string& word){
Node *node = &root;
for(auto ch: word){
int i = ch - 'a';
if(node->children[i] == nullptr){
node->children[i] = new Node;
}
node = node->children[i];
}
node->count += 1;
}
int find(const string& word){
Node *node = &root;
for(auto ch: word){
int i = ch - 'a';
if(node->children[i]){
node = node->children[i];
}else{
return 0;
}
}
return node->count;
}
private:
Node root;
};
class WordsFrequency {
public:
WordsFrequency(vector<string>& book) {
for(auto& word: book){
trie.insert(word);
}
}
int get(string word) {
return trie.find(word);
}
private:
Trie trie;
};