Count higher repetition streak-CodePudding

I've been given this string:

'V--V----V--P--VV---V------V--P--V--V'

I need to define a function that counts the longest streak of '-' in order to find the cost of making a fence. In the case given, it would be 6.

def cost(wall): #calculate the cost of building a wall with fences. the cost will be the longest streak of fences*10
    fence_count = 0
    streak = 0
    for fence in wall:
        if fence == '-':
            fence_count  = 1
        elif fence == fence 1:
            fence_count  = 1
        else:
            streak = fence_count
            fence_count = 0
    return streak*10
                    
wall = input()
c = cost(wall)
print(c)

TypeError: can only concatenate str (not "int") to str

Is there a built-in function in Python that can do this?

CodePudding user response：

Issue

I commented and fixed your code to some extend:

fence_count = 0  # the count can only increase
streak = 0  # direct factor on costs (a fence streak of 1 costs 10)

# count fences (denoted by hyphen char '-')
# iterate through all chars (here variable fence) in a string (here wall)
for fence in wall:
    if fence == '-':  # if fence then increase counter
       fence_count  = 1
    # What if fence_count is now higher than the previous streak ?
    elif fence_count > streak:
        # then we have a new maximum as (new) longest streak
    else:  # else restart counting (e.g. if 'V' or 'P') 
        streak = fence_count  # save counter as streak (only if longer than any streak before?)
        fence_count = 0  # reset counter

    # the longest streak was found
    return streak*10

You cannot add or concatenate (using operator) a character (of type str) in fence to a number (of type int) in numerical literal 1.

Thus the runtime-error

TypeError: can only concatenate str (not "int") to str

here:

    elif fence == fence 1:  # error raised here
       fence_count  = 1

What should the increase and comparison do here?

Alternative solution using regex-split

Using a regex-split, then sort by length descending and finally printing the first (which is the max streak):

import re

line = 'V--V----V--P--VV---V------V--P--V--V'

segments = re.split('[^-]', line)  # split by all non-hyphen chars like V or P
print(segments)  # print the resulting 12 streaks (some empty)
# ['', '--', '----', '--', '--', '', '---', '------', '--', '--', '--', '']

segments.sort(key=lambda s: len(s), reverse=True)  # sorts in-place by length descending
print(segments)  # the longest at first after sorting
# ['------', '----', '---', '--', '--', '--', '--', '--', '--', '', '', '']
print(len(segments[0]))  # print the length of the longest streak
# 6

See also:

Python docs: re.split
Sorting Python list based on the length of the string

CodePudding user response：

You can use max() with a map() function that counts the length of each run of dashes:

from itertools import groupby
max(map(lambda x:sum(1 for c in x[1]) if x[0] == '-' else 0, groupby(data)))

This outputs:

CodePudding user response：

Similar idea with groupby - but in 2 steps: first to find the consecutive range of interesting item, then do 2) len(max(counts)) to get answer.

counts = [list(g) for k, g in groupby(s, key=lambda x: x in ('VP')) if not 
key]

print(counts)   # see what you got

print(len(max(counts)))  # 6

CodePudding user response：

Another variant using regular expressions, find all substrings that match - (i.e. one or more -), map those to their len and get the max:

>>> line = 'V--V----V--P--VV---V------V--P--V--V'
>>> max(map(len, re.findall("- ", line)))
6