Question

2350. Shortest Impossible Sequence of Rolls

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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 that cannot be taken from _rolls.

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

Note that the sequence taken does not have to be consecutive as long as it is in order.

 

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 1

class Solution:
  def shortestSequence(self, rolls: List[int], k: int) -> int:
    ans = 1
    s = set()
    for v in rolls:
      s.add(v)
      if len(s) == k:
        ans += 1
        s.clear()
    return ans

class Solution {
  public int shortestSequence(int[] rolls, int k) {
    Set<Integer> s = new HashSet<>();
    int ans = 1;
    for (int v : rolls) {
      s.add(v);
      if (s.size() == k) {
        s.clear();
        ++ans;
      }
    }
    return ans;
  }
}

class Solution {
public:
  int shortestSequence(vector<int>& rolls, int k) {
    unordered_set<int> s;
    int ans = 1;
    for (int v : rolls) {
      s.insert(v);
      if (s.size() == k) {
        s.clear();
        ++ans;
      }
    }
    return ans;
  }
};

func shortestSequence(rolls []int, k int) int {
  s := map[int]bool{}
  ans := 1
  for _, v := range rolls {
    s[v] = true
    if len(s) == k {
      ans++
      s = map[int]bool{}
    }
  }
  return ans
}