2028. Find Missing Observations 

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class Solution {
    public int[] missingRolls(int[] rolls, int mean, int n) {
        int[] res = new int[n];
        int sum = (rolls.length + n) * mean;
        for (int roll : rolls) {
            sum -= roll;
        }

        if (sum > 6 * n || sum < n) {
            return new int[0];
        }

        int quotient = sum / n, remainder = sum % n;
        for (int i = 0; i < n; i++) {
            res[i] = quotient + (i < remainder ? 1 : 0);
        }
        return res;
    }
}

References

2028. Find Missing Observations