leetcode1268 - Search Suggestions System - medium

Given an array of strings products and a string searchWord. We want to design a system that suggests at most three product names from products after each character of searchWord is typed. Suggested products should have common prefix with the searchWord. If there are more than three products with a common prefix return the three lexicographically minimums products.

Return list of lists of the suggested products after each character of searchWord is typed. 

 

Example 1:

Input: products = ["mobile","mouse","moneypot","monitor","mousepad"], searchWord = "mouse"
Output: [
["mobile","moneypot","monitor"],
["mobile","moneypot","monitor"],
["mouse","mousepad"],
["mouse","mousepad"],
["mouse","mousepad"]
]
Explanation: products sorted lexicographically = ["mobile","moneypot","monitor","mouse","mousepad"]
After typing m and mo all products match and we show user ["mobile","moneypot","monitor"]
After typing mou, mous and mouse the system suggests ["mouse","mousepad"]

Example 2:

Input: products = ["havana"], searchWord = "havana"
Output: [["havana"],["havana"],["havana"],["havana"],["havana"],["havana"]]

Example 3:

Input: products = ["bags","baggage","banner","box","cloths"], searchWord = "bags"
Output: [["baggage","bags","banner"],["baggage","bags","banner"],["baggage","bags"],["bags"]]

Example 4:

Input: products = ["havana"], searchWord = "tatiana"
Output: [[],[],[],[],[],[],[]]

 

Constraints:

• 1 <= products.length <= 1000
• There are no repeated elements in products.
• 1 <= Σ products[i].length <= 2 * 10^4
• All characters of products[i] are lower-case English letters.
• 1 <= searchWord.length <= 1000
• All characters of searchWord are lower-case English letters.

 

prefix相关，用trie：root不包含字符，除此之外，每个node包含一个字符，从root到某个node经过的路径表示一个word。所以每个node指向一串字母集大小的node，为了方便输出，构建trie的时候，每个node里顺便存一下到此为止排序最前的三个word

建树：O(Σlen(product_i))

查询: O(len(searchWord))

 

实现：

class Solution {
public:
    struct TrieNode {
        struct TrieNode* chars[26];
        vector<string> words;
    };
    
    TrieNode* root = new TrieNode();
    
    void insertWord(string& word) {
        TrieNode* p = root;
        for (auto c : word) {
            int idx = c - 'a';
            if (!p->chars[idx])
                p->chars[idx] = new TrieNode();
            p = p->chars[idx];
            if (p->words.size() < 3) {
                p->words.push_back(word);   
            }
        }
    }

    vector<vector<string>> suggestedProducts(vector<string>& products, string searchWord) {
        int n = searchWord.size();
        vector<vector<string>> result(n);
        
        sort(products.begin(), products.end());
        for (auto& product : products)
            insertWord(product);

        TrieNode *p = root;
        for (int i = 0; i < n; i++) {
            int idx = searchWord[i] - 'a';
            if (p->chars[idx]) {
                p = p->chars[idx];
                result[i] = p->words;
            } else
                break;
        }

        return result;
    }
};