Contest Python: ACSL › Checkpoint 2 — Contest 2 Practice
Questions: Checkpoint 2 — Contest 2 Practice
This is a practice paper modelled on ACSL Contest 2: short-answer questions from the four Contest 2 categories, then one programming problem. The Junior paper and the Intermediate/Senior paper share their first four questions, so this checkpoint holds both six-question papers.
| Questions | Category | Division |
|---|---|---|
| 1–2 | Prefix/Infix/Postfix Notation | Junior and above |
| 3–4 | Bit-String Flicking | Junior and above |
| 5–6 | What Does This Program Do? – Looping | Junior |
| 7–8 | LISP | Intermediate and above |
| 9 | Programming problem | Junior and above |
Choose your path.
- Junior: Questions 1–6, then Question 9.
- Intermediate or Senior: Questions 1–4 and 7–8, then Question 9. Questions 5–6 are optional extra loop practice.
- Classroom (no programming): Questions 1–4 and 7–8. Questions 5–6 are optional, and Question 9 is left out.
Take it as a timed practice.
- Put away your notes and set a timer.
- Give yourself 30 minutes for the six-question paper on your path, as in the real contest. Work with pencil and paper only: no computer, no calculator. Write each answer on paper or in your notebook.
- On the Junior, Intermediate or Senior path, then give yourself about 60 minutes for Question 9 (the Classroom path skips it).
Write a complete program that reads the input with
input()and prints exactly the output described. Save it as a.pyfile and run it from a terminal, typing the sample input or feeding it a file:python my_solution.py < sample.txt. Print nothing extra: no prompts ininput(), and no words the problem did not ask for.
These times are a practice pace, not the official rules; the real limits for your division are published by ACSL at acsl.org.
How to write short answers.
- Give exactly one answer, written the way the question asks for it.
- For a prefix or postfix expression, separate the tokens with single spaces and keep the operands in their original order.
- For a numeric value, write a whole number when the value is whole, and otherwise a decimal such as
13.5. - For a bit string, write every bit, at the full length given in the question.
- For a list of bit strings, write them from smallest to largest, separated by a comma and a space.
- For a LISP list, write it in parentheses with single spaces, such as
(A B C), using the capital letters the question uses. - For a program, write exactly the one line it outputs.
When you finish, check yourself.
- Short answers have no sample to test against. Mark the questions you were unsure of, then work each one again by its unit's method: redo the stack or the trace, or turn a conversion back and check that you get the question. Compare with a partner, or with a second attempt made without looking at the first.
- The programming question is checked against its sample, and against inputs of your own made from its constraints: the smallest cases, the largest, and the tricky ones.
Then go back to the unit for any category that cost you points.
Question 1: Moving the Operators Back
Convert the infix expression
A - (B + C) * D ↑ E / Fto postfix.
↑ means "to the power of".
Write the answer as tokens separated by single spaces.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: A postfix expression: one space between tokens (as in `12 3 +`), with the operands kept in their original order. Powers are written `↑`; you may type `^` for `↑`.
Question 2: Evaluate the Prefix
Evaluate the prefix expression
/ - * 12 ↑ 2 3 + 15 * 3 7 + 4 * 2 3↑ means "to the power of".
All operands are whole numbers written in base 10.
Write the value as a number.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Question 3: Flick the Bits
Evaluate the expression
NOT 10110 OR RSHIFT-1 01101 AND LCIRC-2 11010Write the answer as a 5-bit string.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: A bit string at its full length, with the 0s on the left kept (`00110`, not `110`).
Question 4: Solve for x
Find all 5-bit strings x that make this equation true:
x OR 10100 = 10111Write every solution as a 5-bit string, from smallest to largest, separated by a comma and a space.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Every solution in increasing order, each a bit string at its full length (0s on the left kept: `00110`, not `110`), separated by a comma and a space.
Question 5: Paired Up
n = int(input())
total = 0
for i in range(1, n + 1):
for j in range(i, n + 1, 2):
if (i + j) % 3 == 0:
total = total + i * j
print(total)Input
6What exactly does the program print?
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Question 6: Counting Down by Fives
This program is written in ACSL pseudocode.
ACSL papers also write keywords in lowercase, as here.
% is the remainder, / is real division, and int(x) is the greatest integer less than or equal to x.
A for loop includes its end value when the counter reaches it exactly.
input n
c = 0
m = 0
for k = n to 1 step -5
x = k
s = 0
while x > 0
s = s + x % 10
x = int(x / 10)
end while
if s > m then
m = s
end if
c = c + s
next k
output c - mWhat value does the program output when the input value is 47?
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Question 7: Define and Call
Evaluate the last expression, after the first three have been evaluated in order.
(SETQ A 7)
(SETQ B (SUB A 12))
(DEFUN F (X Y) (DIV (ADD (SQUARE X) Y (MULT 2 X)) 4))
(F A B)Write the value of (F A B) as a number.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Question 8: Taking Lists Apart
Evaluate the last expression, after the first one has been evaluated.
(SETQ L '((RED (BLUE GREEN)) (4 5 6) YELLOW))
(REVERSE (CONS (CADDR L) (CADR (CAR L))))Write the value as a LISP list.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: A LISP list: round brackets, single spaces between items, the same capital letters as the question, and no quote mark, as in `(A (B C) D)`.
Question 9: Brackets Away
A fully bracketed infix expression has one pair of brackets round every operator and its two operands, like the first step of the brackets-first method in Unit 4: ((A+B)*(C-(D/E))).
The brackets say exactly which operator is done when, so no order of operations is needed.
The input is one line: a fully bracketed infix expression, with no spaces.
Each operand is one capital letter or one digit, and each operator is +, -, *, / or ^ (the power ↑).
Print two lines: the expression in postfix, and then the expression in prefix, each with its tokens separated by single spaces.
The operands are never worked out: print each one exactly as it is written.
Constraints
- The expression has between 1 and 400 characters.
- Every operator and its two operands are inside exactly one pair of brackets, and there are no other brackets. So an expression that is a single operand has no brackets at all, and any longer expression starts with
(and ends with).
Sample Input
((A+B)*(C-(D/E)))Sample Output
A B + C D E / - *
* + A B - C / D EThe brackets make D/E the first operator done and * the last, so * comes last in the postfix and first in the prefix.
The operands keep their order, A B C D E, in both.
How this is checked: Checked by running your program on 10 test inputs (1 sample, 9 hidden) and comparing its output line by line.