Daily Temperatures

Given a list of daily temperatures `T`, return a list such that, for each day in the input, tells you how many days you would have to wait until a warmer temperature. If there is no future day for which this is possible, put `0` instead.

For example, given the list of temperatures `T = [73, 74, 75, 71, 69, 72, 76, 73]`, your output should be `[1, 1, 4, 2, 1, 1, 0, 0]`.

Note: The length of `temperatures` will be in the range `[1, 30000]`. Each temperature will be an integer in the range `[30, 100]`.

Solution:
This quiz is a classical application of the stack data structure. Here we can store indexes of each element which is waiting a bigger element in a stack, and calculate the difference between the current index and stored indexes when the current element is bigger than previous elements. The while loop part is really elegant and tricky, in which judging whether the stack is empty and comparing elements.

``````class Solution:
def dailyTemperatures(self, T: List[int]) -> List[int]:
ans = [0] * len(T)

stk = list()

for c_index, value in enumerate(T):
while stk and T[stk[-1]] < value:
p_index = stk.pop()
ans[p_index] = c_index - p_index
stk.append(c_index)

return ans``````

Circular Queue

``````class MyCircularQueue:

def __init__(self, k: int):
"""
Initialize your data structure here. Set the size of the queue to be k.
"""
self.tail = -1
self.size = k
self.queue = [None] * self.size

def enQueue(self, value: int) -> bool:
"""
Insert an element into the circular queue. Return true if the operation is successful.
"""
if self.isFull():
return False

if self.isEmpty():

self.tail = (self.tail + 1) % self.size
self.queue[self.tail] = value
return True

def deQueue(self) -> bool:
"""
Delete an element from the circular queue. Return true if the operation is successful.
"""
if self.isEmpty():
return False

self.tail = -1
return True

return True

def Front(self) -> int:
"""
Get the front item from the queue.
"""
if self.isEmpty():
return -1

def Rear(self) -> int:
"""
Get the last item from the queue.
"""
if self.isEmpty():
return -1

return self.queue[self.tail]

def isEmpty(self) -> bool:
"""
Checks whether the circular queue is empty or not.
"""

def isFull(self) -> bool:
"""
Checks whether the circular queue is full or not.
"""
return (self.tail + 1) % self.size == self.head``````

Piles of Boxes

As qualifying people to this event, they hand out an easy algorithm question. Shortly, you need to calculate how less time to move a bunch of boxes in same heigh.

Here is a solution for reference:

``````import collections

def box(boxesInPiles):
sortBoxes = collections.OrderedDict(sorted(collections.Counter(boxesInPiles).items()))
count = 0
for index, key in enumerate(sortBoxes):
count += index * sortBoxes[key]
return count

print(box([4, 5, 5, 2, 4]))``````

Musician

Let’s say there are two persons, Composer and Performer.

The Composer randomly selects three different Pitch which constructed by two part, Note and Octave. Note in the range of “A” to “G”, Octave in the range of “1” to “3”.

For example, here is a typical Pitch combined by ‘A’ and ‘1’, in which ‘A’ is the Note, and ‘1’ is the Octave.

Once Composer selected a Combination, Performer needs to guess it as quick as possible. After each guess, Performer get a feedback which indicates that:

• how many pitches in the guess are included in the target (correct pitches)
• how many pitches have the right note but the wrong octave (correct notes)
• how many pitches have the right octave but the wrong note (correct octaves)

Now, the question is how to get the corrected answer as less times as possible.

``````--  Subject  : UniMelb 2019 SM1 COMP90048 Declarative Programming
--  File     : Proj1.hs
--  Author   : Mingzhe Du
--  Origin   : Mon Apr 8 2019
--  Purpose  : This program for guessing a target chord. In each round of the game,
--             the program will generate a chord from a possible set, and then a feedback
--             against the guess will be given. Depanding on these feedbacks, the aim of this
--             program is get the correct chord with as less as possible guess times.

module Proj1 (Pitch, GameState, toPitch, feedback, initialGuess, nextGuess) where

-- Pitch structure
data Pitch = Pitch { note :: Char,
octave :: Char
} deriving (Eq)
instance Show Pitch where
show (Pitch note octave) = [note, octave]

-- Game State
data GameState = GameState { times :: Int,                  -- Guess times
cCombinations :: [[[Char]]]    -- Possible set
} deriving (Eq, Show)

-- Converting String to Pitch
toPitch :: String -> Maybe Pitch
toPitch (a:b:t)
| not (null t) = Nothing
| (elem note' ['A'..'G']) && (elem octave' ['1'..'3']) = Just Pitch {note = note', octave = octave'}
| otherwise = Nothing
where note' = a
octave' = b

-- Comparing target chord and guessed chord
feedback :: [Pitch] -> [Pitch] -> (Int,Int,Int)
feedback pitch_a pitch_b
| (length pitch_a == 3) && (length pitch_b == 3) = (c_p, c_n - c_p, c_o - c_p)
| otherwise = (0,0,0)
where get_key key = foldr (\x acc -> key x:acc) []
c_p = getCounter pitch_a pitch_b 0                              -- Correct pitches
c_n = getCounter (map note pitch_a) (map note pitch_b) 0        -- Correct notes
c_o = getCounter (map octave pitch_a) (map octave pitch_b) 0    -- Correct Octaves

-- Initial guess
initialGuess :: ([Pitch], GameState)
initialGuess = (currentGuess, gameState)
where currentGuess = combinationToPitch  (cGuess)
gameState = GameState 0 all_combinations
all_items = getCombination "ABCDEFG" "123"
cGuess:all_combinations = subsequencesOfSize 3 all_items        -- New guess and new possible set
getCombination p_note p_octave = foldr (\x acc -> (map (\y -> y:[x]) p_note) ++ acc) [] p_octave
combinationToPitch combinations = map (\(Just x) -> x) \$ map toPitch combinations     -- Converting String to Pitch

-- Get the next guess
nextGuess :: ([Pitch], GameState) -> (Int,Int,Int) -> ([Pitch],GameState)
nextGuess (pGuess, pGameState) pFeedback = (cGuess, cGameState)
where cGuess':cCombs = getNewCombination pGuess pCombinations pFeedback
pCombinations = cCombinations pGameState
cGuess = toChord cGuess'
cGameState = GameState ((times pGameState) + 1) cCombs
toChord = map (\x -> Pitch (x !! 0) (x !! 1))

-- Help Functions

-- remove an item from a list
removeItem :: (Eq a) => a -> [a] -> [a]
removeItem _ [] = []
removeItem x (y:ys)
| x == y = ys
| otherwise = y : removeItem x ys

-- get the number of same elements in two lists
getCounter :: (Eq a) => [a] -> [a] -> Int -> Int
getCounter [] y c = c
getCounter  (x:xs) y c
| elem x y = getCounter xs (removeItem x y) (c+1)
| otherwise = getCounter xs y c

-- Generate combinations by a specifc size
subsequencesOfSize :: Int -> [a] -> [[a]]
subsequencesOfSize n xs = let l = length xs in if n>l then [] else subsequencesBySize xs !! (l-n)
where subsequencesBySize [] = [[[]]]
subsequencesBySize (x:xs) = let next = subsequencesBySize xs in zipWith (++) ([]:next) (map (map (x:)) next ++ [[]])

-- Converting a string list to pitch list
toChord :: [[Char]] -> [Pitch]
toChord a = map (\x -> Pitch (x !! 0) (x !! 1)) a

-- retrive a new guess
getNewCombination :: [Pitch] -> [[[Char]]] -> (Int, Int, Int) -> [[[Char]]]
getNewCombination guess allCombinations pFeedback = foldr (\x acc -> if checkFeedback (toChord x) then  x:acc else acc) [] allCombinations
where checkFeedback nChord = if pFeedback == (feedback guess nChord) then True else False
``````

Here are some Haskell code chunks, which both are simple recursion algorithms.

Quicksort is a sort of poster child for Haskell because everyone does it to showcase how elegant Haskell is.

``````quicksort :: (Ord a) => [a] -> [a]
quicksort [] = []
quicksort (x:xs) =
let smallerSorted = quicksort [a | a <- xs, a <= x]
biggerSoted = quicksort [a | a <- xs, a > x]
in smallerSorted ++ [x] ++ biggerSoted``````
``````maximum' :: (Ord a) => [a] -> a
maximum' [] = error "List is empty!"
maximum' [x] = x
maximum' (x:xs) = (max x (maximum' xs))

replicate' :: Int  -> b -> [b]
replicate' n x
| n <= 0 = []
| otherwise = (x:(replicate' (n-1) x))

take' :: Int -> [a] -> [a]
take' n (x:xs)
| n <= 0 = []
| otherwise = x:(take' (n-1) xs)

reserve' :: [a] -> [a]
reserve' [] = []
reserve' (x:xs) = (reserve' xs) ++ [x]``````

How to swap two variables without extra space

Let’s say, we have two variables, A and B, and our task is swapping these two variables without extra space.

First, we can this:

A = A + B

and,

B = A – B = A + B – B = A (import A from Step 1)

finally,

A = A – B = A + B – A = B (import A, B from Step 1 and 2 respectively)

That’s it, Dude!

Keep going

Listen, smile, agree, and then do whatever the fuck you were gonna do anyway.