Search optimisation in Python - python-3.x

Question

def CountingVallys(PathsTaken):
#Converts the Strings U and D into 1 and -1 respectively
Separate_Paths = [i for i in PathsTaken]
for index, i in enumerate(Separate_Paths):
if i == "D":
Separate_Paths[index] = -1
else:
Separate_Paths[index] = 1
Total_travels = [sum(Separate_Paths[0:i+1]) for i in range(len(Separate_Paths))]
#ValleyDistance shows the indexes where the traveller is below sea level and Valley Depth shows the depth at those
#Indexes
ValleyDistance = []
ValleyDepth = []
for Distance, Depth in enumerate(Total_travels):
if Depth < 0:
ValleyDistance.append(Distance)
ValleyDepth.append(Depth)
#Checks the distance between each index to shows if the valley ends (Difference > 1)
NumberOfValleys = []
DistanceOfValleys = []
TempDistance = 1
for index, Distance in enumerate(ValleyDistance):
# Check if final value, if so, check if the valley is distance 1 or 2 and append the final total of valleys
if ValleyDistance[index] == ValleyDistance[-1]:
if ValleyDistance[index] - ValleyDistance[index - 1] == 1:
TempDistance = TempDistance + 1
DistanceOfValleys.append(TempDistance)
NumberOfValleys.append(1)
elif ValleyDistance[index] - ValleyDistance[index - 1] > 1:
DistanceOfValleys.append(TempDistance)
NumberOfValleys.append(1)
#For all indexes apart from the final index
if ValleyDistance[index] - ValleyDistance[index-1] == 1:
TempDistance = TempDistance + 1
elif ValleyDistance[index] - ValleyDistance[index-1] > 1:
DistanceOfValleys.append(TempDistance)
NumberOfValleys.append(1)
TempDistance = 1
NumberOfValleys = sum(NumberOfValleys)
return NumberOfValleys
if __name__ == "__main__":
Result = CountingVallys("DDUDUUDUDUDUD")
print(Result)
An avid hiker keeps meticulous records of their hikes. Hikes always start and end at sea level, and each step up (U) or down (D) represents a unit change in altitude. We define the following terms:
A valley is a sequence of consecutive steps below sea level, starting with a step down from sea level and ending with a step up to sea level.
Find and print the number of valleys walked through.
In this question I was flagged due to my execution being too long and im wondering if there is any clear optimisations I could make to make it faster. I believe the use of "for-loops" is to blame but im not sure of any other ways to execute my steps.

Answer 1

Total_travels = [sum(Separate_Paths[0:i+1]) for i in range(len(Separate_Paths))]
In above code, why do you want to repeat the computation which you have already performed?
sum(Separate_Paths[0:i+1]) = sum(Separate_Paths[0:i] + Separate_Paths[i+1]
You can make the list Total_travels in efficient manner. That should take care of the too long execution time of your program.
>>> a
[2, 6, 4, 9, 10, 3]
>>> cumulative_sum = []
>>> sum_till_now = 0
>>> for x in a:
... sum_till_now += x
... cumulative_sum.append(sum_till_now)
...
>>> cumulative_sum
[2, 8, 12, 21, 31, 34]
>>>
numpy has a built-in cumsum which I believe to be overkill for your problem.

Answer 2

Here is an alternative solution:
By using a stack it would be easy to find the valleys.
for every new path of the same type ("D" or "U") push it into the stack
Before pushing, check for the last item and if they are opposite then remove it (if(stack[-1]!=path[i]): stack.pop()) from the stack and remember at ( last_path=path[i] )
if the stack is empty so it means there was and cutting with sea level (valley or mountain). If the last path was "U" so it means the was a valley so we count it (if(len(stack)==0): if(last_path=='U'): valleys+=1).
there is a possibility of cutting with the sea level at the end of the path so we need to handle it outside of the loop as well ( if(len(stack)==0 and last_path=='U'): valleys+=1 ).
Here is the code:
def countingValleys(steps, path):
stack=[]
valleys=0
last_path=None
for i in range(len(path)):
if(len(stack)==0):
if(last_path=='U'):
valleys+=1
stack.append(path[i])
else:
if(stack[-1]!=path[i]):
stack.pop()
last_path=path[i]
else:
stack.append(path[i])
if(len(stack)==0 and last_path=='U'):
valleys+=1
return valleys
print(countingValleys(12,"DUDUDUUUUDDDDU"))