Contest Python: ACSL › Unit 3 — What Does This Program Do? (Branching)
Exercises: Unit 3 — What Does This Program Do? (Branching)
Most exercises here are short-answer, just like the What Does This Program Do? questions on an ACSL contest.
- Short-answer (marked short answer): a program and its input are given, either in Python or in ACSL pseudocode.
Trace it by hand and write down exactly what it outputs.
For pseudocode, use ACSL's rules from the dialect table in Lesson 1:
introunds down,FORincludes its end value, and substrings follow ACSL's rules. Every program outputs exactly one line. - Predict, then verify (programming): a program is given in ACSL pseudocode.
First trace it on the sample input and write down your prediction.
Then translate it into a complete Python program that reads the input with
input(), run it on the sample, and compare. Save it as a.pyfile and run it from a terminal:python my_solution.py < assets/ex6/1.in.
Exercises 1–7 are the Junior Branching questions. Exercises 8 onwards trace loops, arrays, grids and strings, which Intermediate and Senior students meet in Contest 1. Each exercise is marked with the lowest ACSL division it belongs to; do every exercise at or below your division. Exercises marked Challenge are extra practice for when you want more.
Exercise 1: First True Branch
score = int(input())
bonus = 0
if score >= 90:
grade = "A"
elif score >= 80:
grade = "B"
bonus = 5
elif score >= 70:
grade = "C"
bonus = 10
else:
grade = "D"
if score + bonus >= 90:
grade = grade + "+"
print(grade, score + bonus)Input
85What exactly does the program print? Work it out by hand first; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 2: Nested Decisions
INPUT x, y
IF x > y THEN
IF x % 2 == 0 THEN
z = x * 2 - y
ELSE
z = x + y * 2
END IF
ELSE
IF y % 3 == 0 || x < 0 THEN
z = y - x
ELSE
z = x * y
END IF
END IF
OUTPUT zInput. x = -4, y = -9
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Exercise 3: Shuffled Digits
n = int(input())
a = n // 100
b = n // 10 % 10
c = n % 10
if a + c == b:
result = n + 1
elif a > c:
if b % 2 == 0:
result = a * 100 + c * 10 + b
else:
result = c * 100 + b * 10 + a
else:
result = n - a - b - c
print(result)Input
734What exactly does the program print? Work it out by hand first; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Exercise 4: Quotient and Leftover
INPUT a, b
q = int(a / b)
r = a - q * b
IF r == 0 THEN
OUTPUT q
ELSE IF q > r THEN
OUTPUT q * 10 + r
ELSE
OUTPUT r ^ 2 - q
END IFInput. a = 47, b = 9
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Exercise 5: Counting the True Tests
a = 6
b = -3
c = 0
count = 0
if a > 0 and b > 0:
count = count + 1
if a > 0 or b > 0:
count = count + 10
if not (c == 0) or a + b == 3:
count = count + 100
if a > 5 or b > 5 and c > 5:
count = count + 1000
if (a > 5 or b > 5) and c > 5:
count = count + 10000
print(count)Input. None: the program reads no input.
What exactly does the program print? Work it out by hand first; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Exercise 6: Parking Fee (predict, then verify)
A car park works out its fee with this ACSL program.
hours is how long the car stayed, and day is the day of the week, from 1 (Monday) to 7 (Sunday).
INPUT hours, day
IF day == 6 || day == 7 THEN
fee = 5
ELSE IF hours <= 2 THEN
fee = 0
ELSE IF hours <= 5 THEN
fee = (hours - 2) * 3
ELSE
fee = 9 + (hours - 5) * 4
END IF
IF fee > 20 THEN
fee = 20
END IF
OUTPUT fee- Predict: trace the program by hand on the sample input and write down what it outputs, before you look at the sample output.
- Verify: translate the program into Python and run it on the sample input.
The input is one line holding hours and day, separated by one space.
Print the fee.
Constraints
0 <= hours <= 241 <= day <= 7
Sample Input
7 3Sample Output
17How this is checked: Checked by running your program on 8 test inputs (1 sample, 7 hidden) and comparing its output line by line.
Exercise 7: One IF After Another
x = 14
y = 0
IF x > 10 THEN
x = x - 6
y = y + 1
END IF
IF x < 10 THEN
x = x * 3
y = y + 1
END IF
IF x % 4 == 0 THEN
x = int(x / 4)
y = y + 1
ELSE
x = x + 1
END IF
OUTPUT x, yInput. None: the program reads no input.
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 8: Stepping Down
total = 0
FOR k = 20 TO 1 STEP -3
IF k % 2 == 0 THEN
total = total + k
ELSE
total = total - 1
END IF
NEXT k
OUTPUT totalInput. None: the program reads no input.
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Exercise 9: Digit Sums Until One Digit
n = int(input())
steps = 0
while n >= 10:
total = 0
while n > 0:
total = total + n % 10
n = n // 10
n = total
steps = steps + 1
print(n, steps)Input
98765What exactly does the program print? Work it out by hand first; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 10: Round Down, Even Below Zero
a = -17
b = 4
c = a / b
d = int(c)
e = int(abs(a) / b)
OUTPUT c, d, eRemember: ACSL's int(x) is the greatest integer less than or equal to x.
Input. None: the program reads no input.
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 11: One Pass of Swaps
The array A starts at position 1 and holds
A(1) = 4, A(2) = 9, A(3) = 2, A(4) = 7, A(5) = 5, A(6) = 8.
n = 6
FOR j = 1 TO n - 1
IF A(j) > A(j + 1) THEN
t = A(j)
A(j) = A(j + 1)
A(j + 1) = t
END IF
NEXT j
OUTPUT A(2), A(4), A(6)Input. None: the array is given above.
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 12: Checkerboard Total
grid = [[3, 8, 1, 6],
[7, 2, 9, 4],
[5, 0, 6, 2]]
total = 0
for r in range(len(grid)):
for c in range(len(grid[0])):
if (r + c) % 2 == 0:
total = total + grid[r][c]
elif grid[r][c] > 5:
total = total - grid[r][c]
print(total, grid[2][1] + grid[1][2])Input. None: the program reads no input.
What exactly does the program print? Work it out by hand first; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 13: Filling a Grid
The 2D array A has rows 1 to 4 and columns 1 to 4.
FOR r = 1 TO 4
FOR c = 1 TO 4
IF r == c THEN
A(r, c) = r * 2
ELSE IF r < c THEN
A(r, c) = c - r
ELSE
A(r, c) = A(r - 1, c) + c
END IF
NEXT c
NEXT r
s = 0
FOR k = 1 TO 4
s = s + A(k, 5 - k)
NEXT k
OUTPUT sInput. None: the program reads no input.
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: a number
Exercise 14: Slices and Swaps
word = input()
first = word[:3]
last = word[len(word) - 3:]
middle = word[2:6]
code = last.upper() + first.lower()
if "a" in middle:
code = code.replace("a", "@")
print(code, middle, len(code))Input
PanoramaWhat exactly does the program print? Work it out by hand first; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 15: Backwards and Pieces
Remember ACSL's substring rules: S[:n] is the first n characters, S[n:] is the last n characters, and S[a:b] is positions a through b, both included.
Positions start at 0.
S = "ACSL CONTEST"
R = ""
FOR j = len(S) - 1 TO 0 STEP -1
R = R + S[j]
NEXT j
T = R[:4] + S[5:7] + R[3:]
OUTPUT TInput. None: the program reads no input.
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 16: Square Steps (predict, then verify)
This ACSL program keeps taking away the largest square number that fits, and counts how many squares it takes away.
INPUT n
count = 0
WHILE n > 0
r = int(sqrt(n))
n = n - r ^ 2
count = count + 1
END WHILE
OUTPUT count- Predict: trace the program by hand on the sample input and write down what it outputs, before you look at the sample output.
- Verify: translate the program into Python, using
math.floorandmath.sqrt, and run it on the sample input.
The input is one line holding the whole number n.
Print the count.
Constraints
1 <= n <= 10000
Sample Input
23Sample Output
5How this is checked: Checked by running your program on 8 test inputs (1 sample, 7 hidden) and comparing its output line by line.
Exercise 17: Perfect Squares Only
import math
total = 0
for n in range(1, 30, 4):
root = math.sqrt(n)
if root == math.floor(root):
total = total + n
else:
total = total - math.floor(root)
print(total, math.sqrt(total + 32))Input. None: the program reads no input.
What exactly does the program print? Work it out by hand first; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.
Exercise 18: A Walk on the Grid
The 2D array A has rows 1 to 3 and columns 1 to 3.
Positions in the string S start at 0.
S = "PYTHON"
FOR r = 1 TO 3
FOR c = 1 TO 3
A(r, c) = (r * 2 + c * 3) % 6
NEXT c
NEXT r
r = 1
c = 1
out = ""
steps = 0
WHILE steps < 6
v = A(r, c)
out = out + S[v]
IF v % 2 == 0 THEN
r = r % 3 + 1
ELSE
A(r, c) = v - 1
c = c % 3 + 1
END IF
steps = steps + 1
END WHILE
OUTPUT outInput. None: the program reads no input.
What exactly is output? Trace it by hand, using ACSL's rules; write the output exactly as it appears.
How this is checked: Checked by comparing your answer with the expected answer.
Answer format: Exactly the one line the program outputs: values separated by one space, strings without quotation marks, and letters in the case the program prints them.