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Day 1: Same Answer, Different Path

01. Same Result, Same Side Effect?

Key Vocabulary (LO AAP-2.L)

Term	Definition (write it)
Algorithm
Result
Side effect
Equivalent algorithms
Boolean expression

One Task, Many Algorithms — Result vs Side Effect

• To compare two algorithms you must check two things: whether they compute the same .
• The CED states that different algorithms can be developed or used to .
• Two algorithms can agree on the result yet still differ because .

Result Is the Value; Side Effect Is What Happens

Result

Side effect

• The RESULT of an algorithm is .
• A SIDE EFFECT is .

Find the Higher Score

One concrete algorithm: compare two scores and display the larger. Its RESULT is 95; its SIDE EFFECT is printing 95.

AP Pseudocode (what the exam tests)

scoreA ← 88
scoreB ← 95
IF(scoreA > scoreB) { higher ← scoreA }
ELSE { higher ← scoreB }
DISPLAY(higher)

Python (the runnable version)

scoreA = 88
scoreB = 95
if scoreA > scoreB:
    higher = scoreA
else:
    higher = scoreB
print(higher)

Output

95

Run and edit this yourself in the coding exercises for this topic.

Similar-Looking, Different Behavior

Two snippets each try to report the higher score. Algo A: IF(a > b){DISPLAY(a)} IF(b > a){DISPLAY(b)}. Algo B: IF(a ≥ b){DISPLAY(a)} ELSE {DISPLAY(b)}. Fill in what each DISPLAYs for each input — watch the tie.

Complete the empty cells.

Input (a, b)	Algo A displays	Algo B displays	Same behavior?
(88, 95)		95	Yes — both print 95
(95, 88)	95	95	Yes — both print 95
(70, 70)			No — A prints nothing on a tie

02. Conditionals ⟷ Boolean Expressions

When an IF Is Just a Boolean in Disguise

• The CED says some conditional statements can be written as .
• IF(cond) { flag ← true } ELSE { flag ← false } is exactly equivalent to .
• The give-away pattern for this equivalence is a conditional whose only job is .

Four Lines That Are Really One

This IF/ELSE is equivalent to the single line passed ← (score ≥ 60). Same result, same side effect.

AP Pseudocode (what the exam tests)

score ← 72
IF(score ≥ 60) { passed ← true }
ELSE { passed ← false }
DISPLAY(passed)

Python (the runnable version)

score = 72
if score >= 60:
    passed = True
else:
    passed = False
print(passed)

Output

true

Run and edit this yourself in the coding exercises for this topic.

Collapse It, or Expand It

Conditional form

Boolean form

• To COLLAPSE a conditional into a Boolean expression (L.3) you .
• To EXPAND a Boolean expression into a conditional (L.4) you .

Match Each Conditional to Its Boolean

Each row is one equivalence. Fill in the missing equivalent form — the two forms must give the same result for every input.

Complete the empty cells.

Conditional form	Equivalent Boolean expression
IF(score ≥ 60) { passed ← true } ELSE { passed ← false }	passed ← score ≥ 60
IF(lives = 0) { gameOver ← true } ELSE { gameOver ← false }
IF(coins ≥ 100) { win ← true } ELSE { win ← false }	win ← coins ≥ 100
IF(NOT ready) { waiting ← true } ELSE { waiting ← false }

Day 2: Building New from Old

01. The Building Blocks You Already Know

Knowing Existing Algorithms Helps You Build New Ones

• Says that knowledge of existing algorithms can help in .
• The four building blocks the CED names are max/min, sum/average, .
• You test whether one integer is evenly divisible by another using .

Largest and Smallest of Two Numbers

The same compare, flipped: > gives the max, < gives the min. With a=88, b=95 the max is 95 and the min is 88.

AP Pseudocode (what the exam tests)

a ← 88
b ← 95
IF(a > b) { largest ← a } ELSE { largest ← b }
IF(a < b) { smallest ← a } ELSE { smallest ← b }
DISPLAY(largest)
DISPLAY(smallest)

Python (the runnable version)

a = 88
b = 95
largest = a if a > b else b
smallest = a if a < b else b
print(largest)
print(smallest)

Output

95 88

Run and edit this yourself in the coding exercises for this topic.

Total and Average of the Scores

Sum first, then divide by how many. Average = 270 / 3 = 90.

AP Pseudocode (what the exam tests)

a ← 80
b ← 90
c ← 100
sum ← a + b + c
average ← sum / 3
DISPLAY(average)

Python (the runnable version)

a = 80
b = 90
c = 100
total = a + b + c
average = total / 3
print(average)

Output

90

Run and edit this yourself in the coding exercises for this topic.

Does a Coin Appear on This Tile?

A coin sits on every 3rd tile. tile MOD 3 = 0 means 3 divides the tile number evenly.

AP Pseudocode (what the exam tests)

tile ← 12
IF(tile MOD 3 = 0)
{ DISPLAY("coin") }
ELSE
{ DISPLAY("no coin") }

Python (the runnable version)

tile = 12
if tile % 3 == 0:
    print("coin")
else:
    print("no coin")

Output

coin

Run and edit this yourself in the coding exercises for this topic.

Trace the Robot's Path Through the Maze

The hero starts at (1,1) facing East (Right). Run the commands in order and fill in the facing and position AFTER each command. On this grid, moving East increases the column; a right turn from East faces South (row increases when moving).

Complete the empty cells.

Step	Command	Facing after	Position after (row, col)
start	—	East	(1, 1)
1	MOVE_FORWARD()	East	(1, 2)
2	MOVE_FORWARD()	East
3	ROTATE_RIGHT()		(1, 3)
4	MOVE_FORWARD()	South

02. Create, Combine, and Modify

Three Ways to Make an Algorithm

• The three ways to create an algorithm are from an idea, by .
• Flipping a working find-max into find-min is an example of creating an algorithm by .
• Feeding a computed sum into a division to get an average is an example of .

Combine Blocks: Average, Then Pass/Fail

The average building block feeds a comparison block: compute the average, then decide pass or fail.

AP Pseudocode (what the exam tests)

s1 ← 80
s2 ← 90
s3 ← 100
avg ← (s1 + s2 + s3) / 3
IF(avg ≥ 60) { DISPLAY("pass") }
ELSE { DISPLAY("fail") }

Python (the runnable version)

s1, s2, s3 = 80, 90, 100
avg = (s1 + s2 + s3) / 3
if avg >= 60:
    print("pass")
else:
    print("fail")

Output

pass

Run and edit this yourself in the coding exercises for this topic.

Modify Blocks: From Max to Min

Original: find the MAX

Modified: find the MIN

• To modify find-max into find-min you change only .
• Modifying a correct algorithm shrinks your testing because .

Why Build from Existing Blocks

• The three benefits of reusing correct building blocks are reducing development time, reducing testing, and .
• Errors in a program built from trusted blocks are most likely to be found .

Common AP Traps

Three ways Topic 3.9 loses points on the exam — one minute now, real points in May.

Result and side effect are not the same — in your own words:

Trace similar-looking code; don't eyeball it — in your own words:

Reuse reduces testing — it does not remove it — in your own words:

Developing Algorithms, in One Slide

• Compare algorithms on TWO axes — same result (value) and same side effect (what is displayed/changed); similar-looking code can still differ.
• A conditional that only stores true/false equals a Boolean expression, and back again.
• Create algorithms from an idea, by combining, or by modifying existing ones; know the building blocks — max/min, sum/average, divisibility via MOD, robot maze path.
• Reusing correct blocks reduces development time, testing, and errors — but the new combination still must be tested.