c$++$Challenge $1$: $($Duplicate Elimination with array$)$ Use a one$-$dimensional array to solve the following problem. Read in $20$ numbers,

each of which is between $1$ to $20.$ As each number is read, validate it and store it in the array only if it isn't a duplicate of a number

already read. After reading all the values, display only the unique values that the user entered. Provide for the "worst case" in which

all $20$ numbers are different. Use the smallest possible array to solve this problem.