Question

642. Design Search Autocomplete System

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Description

Design a search autocomplete system for a search engine. Users may input a sentence (at least one word and end with a special character '#').

You are given a string array sentences and an integer array times both of length n where sentences[i] is a previously typed sentence and times[i] is the corresponding number of times the sentence was typed. For each input character except '#', return the top 3 historical hot sentences that have the same prefix as the part of the sentence already typed.

Here are the specific rules:

• The hot degree for a sentence is defined as the number of times a user typed the exactly same sentence before.
• The returned top 3 hot sentences should be sorted by hot degree (The first is the hottest one). If several sentences have the same hot degree, use ASCII-code order (smaller one appears first).
• If less than 3 hot sentences exist, return as many as you can.
• When the input is a special character, it means the sentence ends, and in this case, you need to return an empty list.

Implement the AutocompleteSystem class:

• AutocompleteSystem(String[] sentences, int[] times) Initializes the object with the sentences and times arrays.
• List<String> input(char c) This indicates that the user typed the character c.
  • Returns an empty array [] if c == '#' and stores the inputted sentence in the system.
  • Returns the top 3 historical hot sentences that have the same prefix as the part of the sentence already typed. If there are fewer than 3 matches, return them all.

 

Example 1:

Input
["AutocompleteSystem", "input", "input", "input", "input"]
[[["i love you", "island", "iroman", "i love leetcode"], [5, 3, 2, 2]], ["i"], [" "], ["a"], ["#"]]
Output
[null, ["i love you", "island", "i love leetcode"], ["i love you", "i love leetcode"], [], []]

Explanation
AutocompleteSystem obj = new AutocompleteSystem(["i love you", "island", "iroman", "i love leetcode"], [5, 3, 2, 2]);
obj.input("i"); // return ["i love you", "island", "i love leetcode"]. There are four sentences that have prefix "i". Among them, "ironman" and "i love leetcode" have same hot degree. Since ' ' has ASCII code 32 and 'r' has ASCII code 114, "i love leetcode" should be in front of "ironman". Also we only need to output top 3 hot sentences, so "ironman" will be ignored.
obj.input(" "); // return ["i love you", "i love leetcode"]. There are only two sentences that have prefix "i ".
obj.input("a"); // return []. There are no sentences that have prefix "i a".
obj.input("#"); // return []. The user finished the input, the sentence "i a" should be saved as a historical sentence in system. And the following input will be counted as a new search.

 

Constraints:

• n == sentences.length
• n == times.length
• 1 <= n <= 100
• 1 <= sentences[i].length <= 100
• 1 <= times[i] <= 50
• c is a lowercase English letter, a hash '#', or space ' '.
• Each tested sentence will be a sequence of characters c that end with the character '#'.
• Each tested sentence will have a length in the range [1, 200].
• The words in each input sentence are separated by single spaces.
• At most 5000 calls will be made to input.

Solutions

Solution 1

class Trie:
  def __init__(self):
    self.children = [None] * 27
    self.v = 0
    self.w = ''

  def insert(self, w, t):
    node = self
    for c in w:
      idx = 26 if c == ' ' else ord(c) - ord('a')
      if node.children[idx] is None:
        node.children[idx] = Trie()
      node = node.children[idx]
    node.v += t
    node.w = w

  def search(self, pref):
    node = self
    for c in pref:
      idx = 26 if c == ' ' else ord(c) - ord('a')
      if node.children[idx] is None:
        return None
      node = node.children[idx]
    return node


class AutocompleteSystem:
  def __init__(self, sentences: List[str], times: List[int]):
    self.trie = Trie()
    for a, b in zip(sentences, times):
      self.trie.insert(a, b)
    self.t = []

  def input(self, c: str) -> List[str]:
    def dfs(node):
      if node is None:
        return
      if node.v:
        res.append((node.v, node.w))
      for nxt in node.children:
        dfs(nxt)

    if c == '#':
      s = ''.join(self.t)
      self.trie.insert(s, 1)
      self.t = []
      return []

    res = []
    self.t.append(c)
    node = self.trie.search(''.join(self.t))
    if node is None:
      return res
    dfs(node)
    res.sort(key=lambda x: (-x[0], x[1]))
    return [v[1] for v in res[:3]]


# Your AutocompleteSystem object will be instantiated and called as such:
# obj = AutocompleteSystem(sentences, times)
# param_1 = obj.input(c)

class Trie {
  Trie[] children = new Trie[27];
  int v;
  String w = "";

  void insert(String w, int t) {
    Trie node = this;
    for (char c : w.toCharArray()) {
      int idx = c == ' ' ? 26 : c - 'a';
      if (node.children[idx] == null) {
        node.children[idx] = new Trie();
      }
      node = node.children[idx];
    }
    node.v += t;
    node.w = w;
  }

  Trie search(String pref) {
    Trie node = this;
    for (char c : pref.toCharArray()) {
      int idx = c == ' ' ? 26 : c - 'a';
      if (node.children[idx] == null) {
        return null;
      }
      node = node.children[idx];
    }
    return node;
  }
}

class AutocompleteSystem {
  private Trie trie = new Trie();
  private StringBuilder t = new StringBuilder();

  public AutocompleteSystem(String[] sentences, int[] times) {
    int i = 0;
    for (String s : sentences) {
      trie.insert(s, times[i++]);
    }
  }

  public List<String> input(char c) {
    List<String> res = new ArrayList<>();
    if (c == '#') {
      trie.insert(t.toString(), 1);
      t = new StringBuilder();
      return res;
    }
    t.append(c);
    Trie node = trie.search(t.toString());
    if (node == null) {
      return res;
    }
    PriorityQueue<Trie> q
      = new PriorityQueue<>((a, b) -> a.v == b.v ? b.w.compareTo(a.w) : a.v - b.v);
    dfs(node, q);
    while (!q.isEmpty()) {
      res.add(0, q.poll().w);
    }
    return res;
  }

  private void dfs(Trie node, PriorityQueue q) {
    if (node == null) {
      return;
    }
    if (node.v > 0) {
      q.offer(node);
      if (q.size() > 3) {
        q.poll();
      }
    }
    for (Trie nxt : node.children) {
      dfs(nxt, q);
    }
  }
}

/**
 * Your AutocompleteSystem object will be instantiated and called as such:
 * AutocompleteSystem obj = new AutocompleteSystem(sentences, times);
 * List<String> param_1 = obj.input(c);
 */