Search Suggestions System

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:


Solution:

class Solution {
    static class TrieNode {
        TrieNode[] children = new TrieNode[26];
        boolean isWord;
        
        public TrieNode() {
            isWord = false;
        }
    }
    
    static class Trie {
        TrieNode root;
        
        public Trie() {
            root = new TrieNode();
        }
        
        public void insert(String s) {
            TrieNode node = root;
            for (int i = 0; i < s.length(); i ++) {
                char c = s.charAt(i);
                if (node.children[c - 'a'] == null) {
                    node.children[c - 'a'] = new TrieNode();
                }
                node = node.children[c - 'a'];
            }
            node.isWord = true;
        }
        
        public List<String> search(String s) {
            List<String> result = new ArrayList();
            TrieNode node = root;
            for (int i = 0; i < s.length(); i ++) {
                char c = s.charAt(i);
                if (node.children[c - 'a'] == null) {
                    return result;
                }
                node = node.children[c - 'a'];
            }
            pre(node, result, s);
            return result;
        }
        
        private void pre(TrieNode root, List<String> result, String prefix) {
            if (root == null) return;
            if (result.size() >= 3) return;
            if (root.isWord) {
                result.add(prefix);
            }
            for (int i = 0; i < 26; i ++) {
                if (root.children[i] != null) {
                    StringBuilder sb = new StringBuilder(prefix);
                    sb.append((char) ('a' + i));
                    pre(root.children[i], result, sb.toString());
                }
            }
        }
    }
        
    public List<List<String>> suggestedProducts(String[] products, String searchWord) {
        List<List<String>> result = new ArrayList();
        Trie trie = new Trie();
        for (String s : products) trie.insert(s);    
        for (int i = 1; i <= searchWord.length(); i ++) {
            String s = searchWord.substring(0, i);
            result.add(trie.search(s));
        }
        return result;
    }
}