2350. Shortest Impossible Sequence of Rolls

Description

You are given an integer array rolls of length n and an integer k. You roll a k sided dice numbered from 1 to k, n times, where the result of the ith roll is rolls[i].

Return the length of the shortest sequence of rolls so that there's no such in rolls.

A sequence of rolls of length len is the result of rolling a k sided dice len times.

 

Example 1:

Input: rolls = [4,2,1,2,3,3,2,4,1], k = 4
Output: 3
Explanation: Every sequence of rolls of length 1, [1], [2], [3], [4], can be taken from rolls.
Every sequence of rolls of length 2, [1, 1], [1, 2], ..., [4, 4], can be taken from rolls.
The sequence [1, 4, 2] cannot be taken from rolls, so we return 3.
Note that there are other sequences that cannot be taken from rolls.

Example 2:

Input: rolls = [1,1,2,2], k = 2
Output: 2
Explanation: Every sequence of rolls of length 1, [1], [2], can be taken from rolls.
The sequence [2, 1] cannot be taken from rolls, so we return 2.
Note that there are other sequences that cannot be taken from rolls but [2, 1] is the shortest.

Example 3:

Input: rolls = [1,1,3,2,2,2,3,3], k = 4
Output: 1
Explanation: The sequence [4] cannot be taken from rolls, so we return 1.
Note that there are other sequences that cannot be taken from rolls but [4] is the shortest.

 

Constraints:

• n == rolls.length
• 1 <= n <= 105
• 1 <= rolls[i] <= k <= 105

 

Solutions

Solution: Greedy

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

 

JavaScript

/**
 * @param {number[]} rolls
 * @param {number} k
 * @return {number}
 */
const shortestSequence = function (rolls, k) {
  const diceSet = new Set();
  let result = 1;

  for (const roll of rolls) {
    diceSet.add(roll);

    if (diceSet.size === k) {
      result += 1;
      diceSet.clear();
    }
  }

  return result;
};