1604. Alert Using Same Key-Card Three or More Times in a One Hour Period

Description

LeetCode company workers use key-cards to unlock office doors. Each time a worker uses their key-card, the security system saves the worker's name and the time when it was used. The system emits an alert if any worker uses the key-card three or more times in a one-hour period.

You are given a list of strings keyName and keyTime where [keyName[i], keyTime[i]] corresponds to a person's name and the time when their key-card was used in a single day.

Access times are given in the 24-hour time format "HH:MM", such as "23:51" and "09:49".

Return a list of unique worker names who received an alert for frequent keycard use. Sort the names in ascending order alphabetically.

Notice that "10:00" - "11:00" is considered to be within a one-hour period, while "22:51" - "23:52" is not considered to be within a one-hour period.

 

Example 1:

Input: keyName = ["daniel","daniel","daniel","luis","luis","luis","luis"], keyTime = ["10:00","10:40","11:00","09:00","11:00","13:00","15:00"]
Output: ["daniel"]
Explanation: "daniel" used the keycard 3 times in a one-hour period ("10:00","10:40", "11:00").

Example 2:

Input: keyName = ["alice","alice","alice","bob","bob","bob","bob"], keyTime = ["12:01","12:00","18:00","21:00","21:20","21:30","23:00"]
Output: ["bob"]
Explanation: "bob" used the keycard 3 times in a one-hour period ("21:00","21:20", "21:30").

 

Constraints:

• 1 <= keyName.length, keyTime.length <= 105
• keyName.length == keyTime.length
• keyTime[i] is in the format "HH:MM".
• [keyName[i], keyTime[i]] is unique.
• 1 <= keyName[i].length <= 10
• keyName[i] contains only lowercase English letters.

 

Solutions

Solution: Hash Table

• Time complexity: O(n)
• Space complexity: O(n)

 

JavaScript

/**
 * @param {string[]} keyName
 * @param {string[]} keyTime
 * @return {string[]}
 */
const alertNames = function (keyName, keyTime) {
  const useKeyCardMap = keyName.reduce((map, name, index) => {
    const times = map.get(name) ?? [];
    const [hour, minute] = keyTime[index].split(':');

    times.push(hour * 60 + +minute);
    return map.set(name, times);
  }, new Map());
  const result = [];

  for (const [name, times] of useKeyCardMap) {
    if (times.length < 3) continue;
    times.sort((a, b) => a - b);

    for (let index = 2; index < times.length; index++) {
      if (times[index] - times[index - 2] > 60) continue;
      result.push(name);
      break;
    }
  }
  return result.sort((a, b) => a.localeCompare(b));
};