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Java-based LeetCode algorithm problem solutions, regularly updated
2028\. Find Missing Observations
Medium
You have observations of `n + m` **6-sided** dice rolls with each face numbered from `1` to `6`. `n` of the observations went missing, and you only have the observations of `m` rolls. Fortunately, you have also calculated the **average value** of the `n + m` rolls.
You are given an integer array `rolls` of length `m` where `rolls[i]` is the value of the ith
observation. You are also given the two integers `mean` and `n`.
Return _an array of length_ `n` _containing the missing observations such that the **average value** of the_ `n + m` _rolls is **exactly**_ `mean`. If there are multiple valid answers, return _any of them_. If no such array exists, return _an empty array_.
The **average value** of a set of `k` numbers is the sum of the numbers divided by `k`.
Note that `mean` is an integer, so the sum of the `n + m` rolls should be divisible by `n + m`.
**Example 1:**
**Input:** rolls = [3,2,4,3], mean = 4, n = 2
**Output:** [6,6]
**Explanation:** The mean of all n + m rolls is (3 + 2 + 4 + 3 + 6 + 6) / 6 = 4.
**Example 2:**
**Input:** rolls = [1,5,6], mean = 3, n = 4
**Output:** [2,3,2,2]
**Explanation:** The mean of all n + m rolls is (1 + 5 + 6 + 2 + 3 + 2 + 2) / 7 = 3.
**Example 3:**
**Input:** rolls = [1,2,3,4], mean = 6, n = 4
**Output:** []
**Explanation:** It is impossible for the mean to be 6 no matter what the 4 missing rolls are.
**Constraints:**
* `m == rolls.length`
* 1 <= n, m <= 105
* `1 <= rolls[i], mean <= 6`