This is an information sheet on functions/python methods you'll be using as you solve the questions! Some functions are built into python, whilst others are imported into the files as a provided function!
Inbuilt into Python. Just like any other programming languanges, Python has loops built it to it. For this section, we will be focusing solely on for loops.
for i in range(10):
print(i)
In general, there are 4 components that define a for loop.
- The
forkeyword indicates that we are defining aforloop - The
iindicates the counter - And the
rangeindicates... well... the range. Basically how far the loop is gonna go - After the
:, any code below this line that is indexed some tab space in is the logic/code that will be repeated. In the example, this logic is simplyprint(i)
Much like other programming languages, Python is zero indexed, meaning that numbers start from 0 instead of 1. Meaning that declaring range(10) actually gives you 0-9 instead of 1-10.
Inbuilt into Python. List splicing refers to the process of extracting subset(s) from a list or array. This basically allows you to select sections or portions of a list.
Let's say you have the word pineapple. You splice your pineapple and extract the word apple. This is basically list splicing, but instead of fruits, you are splicing arrays and lists.
fruit = ["p", "i", "n", "e", "a", "p", "p", "l", "e"]
apple = fruit[4:8:1]
print(apple)
To list splice, simply refer to your list and in square brackets declare your starting index, ending index and your step. So, you get something like: list[start:stop:step].
Note that the stop index is exclusive. This means that for example from pineapple you want to splice the string "pine". Since the ending letter 'e' is in index 3, you would want to stop at 4 since the stop index is not inclusive.
Inbuilt into Python. str() transforms whatever you input into a string.
number = 10
string = str(10)
In this example, the string variable represents a string value equal to "10".
Inbuilt into Python. Similar to splicing, split() allows you to split a list/array into multiple different sections.
fullName = "Robert Downey Jr."
splitName = fullName.split(" ")
print(splitName) # ['Robert', 'Downey', 'Jr.']
The split() function takes in a separator which indicates at what characters you want to split. This case, we split when we encounter a whitespace. Note that split() can also take a second optional argument. This second argument represents the number of splits you can do before stopping.
fullName = "Robert Downey Jr."
splitName = fullName.split(" ", 1)
print(splitName) # ['Robert', 'Downey Jr.']
Provided function. Allows you to find all prime numbers up to a certain give number, n. Prime numbers start at 2.
primes = generate_primes(12)
print(primes) # [2,3,5,7,11]
Provided function. Goes through all the index of a list from start to finish and returns the index of the value if the value is found. Will return -1 if the value is not found
list = [33,45,12,4,5,3,987,42]
indexOfTwelve = linear_search(list, 12)
print(indexOfTwelve) # 2
Note: Binary search will only properly work when the given list is sorted (preferably in ascending order)
Provided function. Binary search has the same purpose as linear_search but faster. The only downside is that in order to work properly, the given list must be ordered.
Binary search works by first splitting down the midpoint of the list, they see if the current value is lower or greater than the target value. If greater, they dispose of everything on their left and vice versa if the current value is lower. This repeats until there is only one value left.
list = [12,17,23,29,56,76,77,98]
indexOfSeventeen = binary_search(list, 17)
print(indexOfSeventeen) # 1
A detailed view:
target = 17
original_list = [12,17,23,29,56,76,77,98]
^ ^ ^
L M R
** 56 is bigger than 17, take the left! **
first_step = [12,17,23,29]
^ ^ ^
L M R
** 23 is bigger than 17, take the left! **
second_step = [12,17]
^ ^
L M and R
** Current M = 17, found!
return indexOf(17)
Provided function. Max Subarray is a function that returns the maximum sum subarray of an array. Basically, in a list of integers, this functions returns the subarray which makes up the largest sum.
For the array [1, -2, 3, 5, -1, 2], the function would return the subarray [3, 5, -1, 2], which has the maximum sum. No other combinations of adjacent numbers make a sum bigger than 3 + 5 - 1 + 2 = 9
list = [1, -2, 3, 5, -1, 2]
maxSubarray = max_subarray(list)
print(maxSubarray) # [3, 5, -1, 2]