Class 29 — Friday, April 1

Problem solving at its best

The Magnificent – Seven problems for practice – Let's do them today

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Look both ways

• Back or ahead

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Agenda

• Being functional

• Mindful collaboration

• Appreciation for buddying

• Better able to convert problem specifications into working functions

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Paired Programming

• Paired Programming

• Paired programming is very specific about who is typing when:

• One person poses as the navigator, who is not typing-- this is the person who pitches ideas about how to solve problems, or what line of code to add next.

• One person is the driver, and they are the only person touching the keyboard. This person is often listening to the ideas that the navigator is laying out, maybe catching a few errors, and translating actions into code.

• Today, we require that you switch roles at least once, halfway through the class. You are welcome to switch more often!

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Requirements

• The buddy system is required for this effort.

• None of the functions you develop should get user-typed input or print any output.

• Examine and think about algorithms for the problems. However, do not write any code before class.

• My module file magnificent.py must be used.

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Module magnificent.py

• Implements seven functions most of which are related to tasks performed this semester.

• Module file magnificent.py

• Tester program seven.py

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Function future_me( a, y )

• Returns how a person whose a years-old will be in the year y. You can assume the current year is 2022.

• Partial output from a sample run of seven.py

a 20 year-old will be 84 in 2086

a 19 year-old will be 96 in 2099

• Possible algorithm

• Compute difference between 2021 and y.

• The future age is total of a and the difference.

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Function manhattan_distance( a1, s1, a2, s2 )

• Returns the approximate distance in miles between a person at the corner avenue a1 and street s1 in Manhattan and a person at the corner of avenue a2 and street s2 in Manhattan.

• NYC distance rules:

• Distance of a Manhattan city block running from one street to the next is on average 1/20^th of a mile.

• Distance of a Manhattan city block running from one avenue to the next is on average 3/20^th of a mile.

• For example, if you were to run the two locations from the map above, you should get the output "Corners ( 1 , 55 ) and ( 3 , 51 ) are 0.5 miles apart." This is because getting from 1st to 3rd avenue contributes 0.3 miles, and the distance from 55th to 51st street adds 0.2 miles. So the function ran at the map's arguments manhattan_distance( 1, 55, 3, 51 ) should return 0.5.

• Partial output from a sample run of seven.py

Corners ( 6 , 59 ) and ( 7 , 34 ) are 1.4 miles apart

Corners ( 2 , 47 ) and ( 6 , 238 ) are 10.15 miles apart

• Possible algoithm

• Compute absolute value of the street differences

• Compute absolute value of the avenue differences

• The distance between the two locations is the street difference multiplied by 1/20 plus the avenue difference multiplied by 3/20.

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Function relate( x, y )

• Returns '<', '==', or '>', depending whether the relationships between strings x and y are respectively:

• x alphabetically comes before y,

• x is equal to y, or

• x alphabetically comes after y.

• Note: in comparing x and y letter case does not matter

• Partial output from a sample run of seven.py

kiwi == Kiwi

apple < banana

orange > melon

• Possible algorithm

• Convert x and y into lower case equivalents.

• Determine which case applies: x comes before y, x equals y, or x comes after y.

• Return respectively '<', '==', or '>' depending upon the possible relationships

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Function youngest( y )

• Returns the youngest acceptable age for a y year-old to date according to the dating folk rule that you should only date someone who is at least seven years older than than half your age.

• Partial output from a sample run of seven.py

a 19 year-old can date a 16 year-old

a 22 year-old can date a 18 year-old

• Possible algorithm

• Compute and return y divided by 2 plus 7 using integer arithmetic

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Function is_dateable( y1, y2 )

• Returns True or False whether a y2 year-old is an acceptably-aged date for a y1year-old.

• Your implementation should make use of function youngest().

• Partial output from a sample run of seven.py

a 15 year-old can date a 22 year-old is True

a 22 year-old can date a 15 year-old is False

a 19 year-old can date a 18 year-old is True

• Possible algorithm

• Determine minimum dateable age for y1

• Return whether or not y2 is at at least that minimum dateable age of y1

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Function mutually_dateable( y1, y2 )

• Returns True or False whether both a y2 year-old is an acceptably-aged date for a y1 year-old, and a y1 year-old is an acceptably-aged date for a y2 year-old

• Your implementation should make use of function is_dateable().

• Partial output from a sample run of seven.py

a 25 year-old can date a 65 year-old and vice-versa is False

a 20 year-old can date a 18 year-old and vice-versa is True

• Possible algorithm

• Determine whether y1 is dateable for y2.

• Determine whether y2 is dateable for y1.

• Return whether both dateable conditions are true.

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Function middle( s )

• If the length of s is odd, the function returns the middle character of s; otherwise, the function returns the two middle characters of s.

• Partial output from a sample run of seven.py should be.

Middle of abcde is c

Middle of abcdef is cd

Middle of abcd is bc

• Questions

• How does the remainder operator % help you check whether a number is odd?

• Suppose n is the length of s and m is is n // 2.

• If n is odd, what is the middle index of s?

• If n is even, what are the middle indices of s?

• Possible algorithm

• Determine the length of s

• Use your answer to first question above to test whether the length of s is odd.

• Use your answer to the second question above to determine the result.

• Return the result.

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🦆 © 2022 Jim Cohoon

Resources from previous semesters are available.