CB 3.3, 3.4 • 9 min read

Alogrithims

Definition: A finite set of instructions to accomplish a task

Algorithim Basics

Sequence: Follows a sequence of steps

Selection: choose different outcomes at steps based on a condition that is made

Iteration: Repetition of code segment if condition is met

Psuedo Code

Definition: A planning language/text that conveys the general implementation of an algorithim to all programers

Sample College Board Psuedo Code(Strings):

Robot MCQ(Algorithims)

Develop an general algorithm that allows the robot in EVERY box to go around the black rectangular box once, back to its original starting point.

String Operations

Length function gives the length of a string

Python Example/Pseudo Code example: len(“codecodecode”) returns 12

String Concatenation is similar to adding strings together

Pseudo Code: Concat(“String1 ”,”String2”) returns “String1 String2”

Python Code: “String1 “+”String2” concatenates the strings together

String substringing can collect a range of character from a string

Pseudo Code: substring(“MortensonBest”,1,4) returns Mort

PythonCode: string=”MortensonBest”

                       string[0:4] returns “Mort”

String Algorithims

Palindrome

Takes user input and converts to a palindrome by duplicating the string backwards. Users can choose to duplicate last character or not.

Constraints: defaults to no duplication unless user types exactly “yes”

A palindrome string or number is the same read forwards or backwards. Simple as that.

Ex.

“bob”

“hannah”

1337331

9

Example of Palindrome Algorithim Used:

Takes user input and converts to a palindrome by duplicating the string backwards. Users can choose to duplicate last character or not.

Constraints: defaults to no creation of palindrome unless user types exactly “yes”

mystr = str(input("Enter your string: "))
mybool = input("Would you like to make a palindrome with this string?").lower()

if mybool == "yes":
    secondstr = mystr[::-1]
else:
    secondstr = mystr[:-1]
    secondstr = secondstr[::-1]
endresult = mystr+secondstr
print(endresult)

Enter your string: String
Would you like to make a palindrome with this string?Yes
StringgnirtS

Popcorn Hack: Write steps for an algorithim that can find the index of any character in a string

Example: Input: “C” String <- “ABCDEFG”

Output: 2

Answer

1. Collect Input Character and Define String
2. Compare current character of String with Input
3. If they are same output the index otherwise repeat step 2 again until they are the same

Homework Hack For String Algorithims

Write Python Code or Psuedo Code that is able to take a string as input and tell if its a palindrome

Math Algorithims

Fibonacci Sequence

Prints the first n fibonacci numbers in a list Constraints: n > 1

f0 = 0
f1 = 1
fiblist = [f0,f1]
r = int(input("How many items do you want in your fibonacci sequence? Enter a number 2 or greater"))
for i in range(r-2):
    x = fiblist[-1]
    y = fiblist[-2]
    fiblist.append(x*y) # Add the sum of the previous 2 numbers to the list
print(fiblist)

How many items do you want in your fibonacci sequence? Enter a number 2 or greater3
[0, 1, 0]

Popcorn Hack: Can anybody tell how we can fix this code so it correctly makes a fibonacci sequence?

Sorting Algorithims

Sorts an array of integers in increasing order. Relatively inefficient, however.

array = [3,5,6,1,4,2]
n = len(array)
for i in range(n):
    for j in range(0,n-i-1):
        if array[j] > array[j+1]:
            array[j], array[j+1] = array[j+1], array[j]
print(array)

[1, 2, 3, 4, 5, 6]

Selection Sort

Homework Hack 2

Create a program that at least 2 of the algorithmic concepts covered in this notebook.