LeetCode每日一题(2350. Shortest Impossible Sequence of Rolls)

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

如果 rolls[…i]包括所有数字, 那我们就可以从中挑出所有长度为 1 的组合, 再进一步, 如果 rolls[i…j]也包括所有数字,那我们就可以从 rolls[…j]中可以挑出所有长度为 2 的组合, 以此类推如果 rolls[j…k]也包括所有数字, 那我们就可以从 rolls[…k]中挑出所有长度为 3 的组合。我们要做的就是找到尽可能小的 i,j,k。直到我们无法再找出下一个包括所有数字的 section 为止



use std::collections::HashSet;

impl Solution {
    pub fn shortest_sequence(rolls: Vec<i32>, k: i32) -> i32 {
        let mut exists = HashSet::new();
        let mut ans = 1;
        for n in rolls {
            exists.insert(n);
            if exists.len() == k as usize {
                exists.clear();
                ans += 1;
            }
        }
        ans
    }
}

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