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#2534 - Time Taken to Cross the Door

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Array Simulation Queue

Problem Description

There are n persons numbered from 0 to n - 1 and a door. Each person can enter or exit through the door once, taking one second.

You are given a non-decreasing integer array arrival of size n, where arrival[i] is the arrival time of the ith person at the door. You are also given an array state of size n, where state[i] is 0 if person i wants to enter through the door or 1 if they want to exit through the door.

If two or more persons want to use the door at the same time, they follow the following rules:

  • If the door was not used in the previous second, then the person who wants to exit goes first.
  • If the door was used in the previous second for entering, the person who wants to enter goes first.
  • If the door was used in the previous second for exiting, the person who wants to exit goes first.
  • If multiple persons want to go in the same direction, the person with the smallest index goes first.

Return an array answer of size n where answer[i] is the second at which the ith person crosses the door.

Note that:

  • Only one person can cross the door at each second.
  • A person may arrive at the door and wait without entering or exiting to follow the mentioned rules.

Solution

/**
 * @param {number[]} arrival
 * @param {number[]} state
 * @return {number[]}
 */
var timeTaken = function(arrival, state) {
  const enterPool = [];
  const exitPool = [];
  let currentTime = 0;
  let previousState = 1;
  let i = 0;
  const result = new Array(arrival.length);

  while (i < arrival.length || enterPool.length > 0 || exitPool.length > 0) {
    while (i < arrival.length && arrival[i] <= currentTime) {
      if (state[i] === 0) {
        enterPool.push(i);
      } else {
        exitPool.push(i);
      }
      i++;
    }

    if (previousState === 1) {
      if (exitPool.length > 0) {
        result[exitPool.shift()] = currentTime;
      } else if (enterPool.length > 0) {
        result[enterPool.shift()] = currentTime;
        previousState = 0;
      }
    } else {
      if (enterPool.length > 0) {
        result[enterPool.shift()] = currentTime;
      } else if (exitPool.length > 0) {
        result[exitPool.shift()] = currentTime;
        previousState = 1;
      } else {
        previousState = 1;
      }
    }

    currentTime++;
  }

  return result;
};