CODEWITHSUNDEEP
pythonpython-3.x
kreativv
kreativv

Reputation: 13

Counting how much number are in ascending order in a row

I need to write function that will count how much numbers are ordered in ascending order in a row. for example: we have this list:

L = [2, 4, 5, 6, 7, 2, 3, 2, 2, 2, 8, 7, 5, 6]

and the largest ascending series of numbers are 5.

I've tried:

count=0
def ascord(L,count):
    for i in range(0,len(L)-1):
        if L[i]<L[i+1]:
            count+=1
    return count

but the output is 7. I don't know how to "reset" count so it wouldn't take [2,8] and [5,6] into consideration

Edit: I meant that if I for ex. add at the end of list twenty numbers in asc. order they will be largest series of numbers, so the first count should be set to 0, and start counting from start

PS. Sorry for my english.

Upvotes: 0

Views: 849

Answers (5)

Grijesh Chauhan
Grijesh Chauhan

Reputation: 58291

Your code instead counts the number of pairs in the list L such that L[i] < L[i + 1]. The bug is that you do not track the continuity of ascending sub-sequence in the list. For example, while iteration over L if at some point a condition L[i] >= L[i + 1] occur then you should reset count. @Gareth Ma corrected your code. Although, below I have shared my code that will return you max length ascending subsequence in the list L.

Note, while iterating over the L, cstart and cend are index points for the current subsequence. Current subsequence grows until the current value cval greaser than previous val — keeps track of increasing value. At the end of each subsequence (either because of iteration exhaust or the current cval is smaller than previous val) I compare the lengths of subsequences and rests start and end indexes of longest subsequences in L.

def find_longest_ascending(L):
    if len(L) < 2:
        return L
    I = enumerate(L)
    cstart, val = next(I)
    start = end = cstart
    for cend, cval in I:
        if cval <= val:
            if end - start < cend - cstart:
               start, end = cstart, cend
            cstart = cend
        val = cval
    if end - start < cend - cstart + 1:
       start, end = cstart, cend + 1
    return L[start: end]

When the longest ascending subsequence is the suffix of the L (in if-condition outside the for-loop) the cend do not point out of subsequence hance added 1.

Upvotes: 0

andreis11
andreis11

Reputation: 1151

Edited:

Inspired from here.

sub_lst = [0]+[i for i in range(1,len(L))  if L[i] < L[i-1] ]+[None]
print(max(len(x) for x in (L[b:e] for (b, e) in ((0,1) if sub_lst[1] == None else (sub_lst[i-1],sub_lst[i]) for i in range(1,len(sub_lst))))))

Unreadable, I know. Took it as a challenge :)

Upvotes: -2

dawg
dawg

Reputation: 104092

With groupby you can find the longest sequence of elements that sort ascending:

L = [2, 4, 5, 6, 7, 2, 3, 2, 2, 2, 8, 7, 5, 6]

from itertools import groupby 

sorted_seq=[]
for k,v in groupby(zip(L, L[1:]), key=lambda t:t[0]<t[1]):
    if k==True: 
        temp=list(v)
        sorted_seq.append([t[0] for t in temp]+[temp[-1][1]])

>>> sorted_seq
[[2, 4, 5, 6, 7], [2, 3], [2, 8], [5, 6]]

Then take the max of that with len as a key:

>>> max(sorted_seq, key=len)
[2, 4, 5, 6, 7]

Then:

>>> len(max(sorted_seq, key=len))
5

Which (if you don't care about dropping the final element of the sorted sequence and adding 1 to compensate) can be a single comprehension: 

>>> len(max(([t[0] for t in v] for k,v in groupby(zip(L, L[1:]), key=lambda t:t[0]<t[1]) if k), key=len))+1
5

Upvotes: 1

tandontburn
tandontburn

Reputation: 71

According to your logic, start with

count = 1

instead of

count = 0

Also, use an additional variable to keep track of the max count encountered so far, while traversing through the list. Reset count to 1 when the ascent breaks.

def ascord(L):
    count, ans = 1, 1     
    for i in range(len(L) - 1):
        if L[i]<L[i+1]:
            count+=1
        else:
            count=1
        ans = max(count, ans)
    return ans

Upvotes: 1

Gareth Ma
Gareth Ma

Reputation: 707

Cleaned up:

def ascord(L):
    answer = 0
    count = 1
    for i in range(len(L) - 1):
        if L[i] < L[i + 1]:
            count += 1
        else:
            if count > answer:
                answer = count
            count = 1
    return max(count, answer)

L = [2, 4, 5, 6, 7, 2, 3, 2, 2, 2, 8, 7, 5, 6]
print (ascord(L)) # 5

cheers :)

Upvotes: 2

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