Four Core Patterns

The AP exam tests these patterns repeatedly. Recognize and write each one instantly.

• Accumulator: total=0; for each item: total+=item
• Counter: count=0; for each item: if condition: count+=1
• Min/Max: Initialize with first element; loop, compare, update
• Linear Search: Loop through list; return index when target found

nums = [4, 9, 2, 7, 5]
minimum = nums[0]
for n in nums:
    if n < minimum:
        minimum = n
print(minimum)  # 2

nums <- [4, 9, 2, 7, 5]
minimum <- nums[1]
FOR EACH n IN nums
{
    IF n < minimum
    { minimum <- n }
}
DISPLAY(minimum)

Combining Patterns

Complex problems decompose into simpler patterns. Average = accumulate sum + count elements + divide. Exam strategy: ask which of the 4 patterns this problem needs.

Practice Problems

data <- [3,8,2,9,5,8]
count <- 0
FOR EACH n IN data
{
    IF n > 6
    { count <- count + 1 }
}