【leetcode】1268. Search Suggestions System

题目如下：

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
• 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.

解题思路：首先对products排序，接下来把每个product存入字典树中，字典树每个节点除了保存子节点的地址之外，还存前三个前缀能映射到该节点的product。

代码如下：

class TreeNode(object):
    def __init__(self,val):
        self.val = val
        self.child = {}
        self.top3 = []
class Trie(object):
    def __init__(self):
        self.root = TreeNode(None)
    def add(self,word):
        node = self.root
        for i in word:
            if i not in node.child:
                child_node = TreeNode(i)
                node.child[i] = child_node
            if len(node.top3) < 3:
                node.top3.append(word)
            node = node.child[i]
        if len(node.top3) < 3:
            node.top3.append(word)

    def search(self,prefix):
        node = self.root
        for i in prefix:
            if i not in node.child:
                return []
            node = node.child[i]
        return node.top3



class Solution(object):
    def suggestedProducts(self, products, searchWord):
        """
        :type products: List[str]
        :type searchWord: str
        :rtype: List[List[str]]
        """
        products.sort()
        trie = Trie()
        for product in products:
            trie.add(product)
        res = []
        word = ''
        for char in searchWord:
            word += char
            res.append(trie.search(word))

        return res