I got this assignment and the way it is worded is confusing to me. If anyone can explain it better it would be a great help also how to approach the problem

Use a one dimensional array to solve the following problem. Read in 20 numbers, each of which is between 10 and 100, inclusive. As each number is read, print it only if it is not a duplicate of a number already read. Provide for the “worst case” in which all 20 numbers are different. Use the smallest possible array to solve this problem.

Should I use an array of 20 and what does it mean by use the smallest possible array?