#925 · #2028 · Find Missing Observations(找出缺失的观测数据)

Given an array rolls of m dice observations (each in 1..6) plus integers mean and n, the n + m total observations average exactly mean. Return any length-n array of missing observations, each in 1..6, or an empty array if none exists. Constraints: 1 <= n, m <= 10^5, 1 <= mean <= 6, 1 <= rolls[i] <= 6.