Search and Sort Like a Computer

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Technology and Computer Science · Computer Science
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Page 2
Search and Sort Like a Computer
Technology and Computer Science · Computer Science · Grades 7-9 · 50 minutes
Time needed
50 minutes (one class period)
Prep
Copy the 2-page worksheet (one per student). Write the “guess the middle” rule on the board.
Technology
None.
Student
independence
High. Students work alone, then compare with a partner.
Copies to make
One 2-page worksheet per student
Materials
Pencils, Worksheet, Whiteboard or chalkboard
Goal for today: Students will find rules in number patterns, trace a halving search on a sorted list, and sort a list by
comparing neighbors.
Before the bell
☐ Copy the worksheet, one per student (2 pages).
☐ Write on the board: Guess the middle rule: look at the middle value. If your target is smaller, keep the left
half. If it is bigger, keep the right half. Repeat.
☐ Write the example: a secret number from 1 to 10. Guess 5. “Higher.” Now it is 6 to 10, so guess 8. “Lower.”
Now it is 6 or 7.
☐ Keep the answer key on your desk.
Say this to start
Computers handle huge amounts of data, so they need smart ways to find and organize it. Today you will use patterns,
then two real algorithms: one for finding an item quickly and one for putting items in order. Everything you need is on
the worksheet and the board. Work step by step and use your pencil to cross out values that are no longer possible.
Run of show
Minutes
What you do
What students do
0–5
Take attendance. Hand out the worksheet.
Read the introduction box.
5–13
Read the guess-the-middle rule and the example from the
board aloud. Ask: “Why is guessing the middle smarter
than guessing 1, then 2, then 3?” Take one or two answers.
Discuss briefly and follow along.
13–23
Tell students to do Part A (questions 1 through 4), the
number patterns.
Find the rule and write the next number in
each pattern.
23–38
Tell students to do Part B and C (questions 5 through 10)
about searching.
Use the middle rule to search a list and
count the checks.
38–46
Tell students to do Part D (the sorting table and questions
11 and 12).
Sort a list by comparing neighbors and
recording each pass.
46–50
Collect all worksheets. If time allows, read a few answers
aloud.
Hand in the paper.


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Technology and Computer Science · Computer Science
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Page 3
If things go wrong
• If students are not sure how to find the middle of a list, tell them to cross off the same number of values from
each end until one is left.
• If students disagree on a pattern, ask them to check the rule on every number in the pattern.
• If someone misses the sorting pass idea, use the board: compare the first two numbers, swap if the left is
bigger, then move one step right.
• If students finish early, use the early finisher list.
Early finishers
• Make your own number pattern with a rule. Write the first five numbers and trade with a partner.
• Pick a number from 1 to 100 and describe the guesses someone would need to find it using the middle rule.
Support and challenge
• Support: Let students cross out the numbers that are ruled out in each step. Have them do questions 1, 2, 5,
6, 8 and 11.
• Challenge: Ask students to explain why the middle rule needs a sorted list and what would go wrong with an
unsorted one.
Notes for the teacher (you fill this in)
Jot a few lines before you leave. A full Daily Sub Report is in the free Sub Survival Kit at SubstitutePlans.com.
How far the class got / what to pick up next:
Students who were especially helpful:
Anything the teacher should know: