CODEWITHSUNDEEP
python-2.7
Nahua Kang
Nahua Kang

Reputation: 406

Codeeval Challenge 230: Football, Answer Only Partially Correct

I am working on a relatively new challenge in CodeEval called 'Football.' The description is listed in the following link: https://www.codeeval.com/open_challenges/230/

Inputs are lines of a file read by Python, and within each line there are lists separated by '|', with each list representing a country: the first being country "1", second being country "2", and so on.

1 2 3 4 | 3 1 | 4 1

19 11 | 19 21 23 | 31 39 29

Outputs are also lines in response to each line read from the file.

1:1,2,3; 2:1; 3:1,2; 4:1,3;

11:1; 19:1,2; 21:2; 23:2; 29:3; 31:3; 39:3;

so country 1 supports team 1, 2, and 3 as shown in the first line of output: 1:1,2,3.

Below is my solution, and since I have no clue why the solution only works for the two sample cases lited in the description link, I'd like to ask anyone for comments and hints on how to correct my code. Thank you very much for your time and assistance ahead of time.

import sys

def football(string):
    countries = map(str.split, string.split('|'))
    teams = sorted(list(set([i[j] for i in countries for j in range(len(i))])))
    results = []
    for i in range(len(teams)):
        results.append([teams[i]+':'])
        for j in range(len(countries)):
            if teams[i] in countries[j]:
                results[i].append(str(j+1))
    for i in range(len(results)):
        results[i] = results[i][0]+','.join(results[i][1:])
    return '; '.join(results) + '; '
            
if __name__ == '__main__':
    lines = [line.rstrip() for line in open(sys.argv[1])]
    for line in lines:
        print football(line)

Upvotes: 0

Views: 59

Answers (2)

Blckknght
Blckknght

Reputation: 104722

Here's how I solved it:

import sys

with open(sys.argv[1]) as test_cases:
    for test in test_cases:
        if test:
            team_supporters = {}
            for nation, nation_teams in enumerate(test.strip().split("|"), start=1):
                for team in map(int, nation_teams.split()):
                    team_supporters.setdefault(team, []).append(nation)
            print(*("{}:{};".format(team, ",".join(map(str, sorted(nations))))
                    for team, nations in sorted(team_supporters.items())))

The problem is not very complicated. We're given a mapping from nation (implicitly numbered by their order in the input) to a list of teams. We need to reverse that to create an output that maps from a team to a list of nations.

It seems natural to use a dictionary that maps in the same way as the desired output. We can use enumerate to give numbers to the nations as we iterate over them. The setdefault method of the dict adds empty lists to the dictionary as they are needed (using a collections.defaultdict instead of a regular dictionary would be another way to deal with this). We don't need to care about the order of the input, nor the order things are stored in the dictionary's inner lists.

The output we build using str.format calls and the default space separator of the print function. If the final semicolon wasn't desired, I'd have used print("; ".join("{}:{}.format(...))) instead. Since the output needs to be sorted by team at the top level, and by nation in the inner lists, we make some sorted calls where necessary.

Sorting the inner lists is probably not even be necessary, since the nations were processed in order, with their numbers derived from the order they had in the input line. Fortunately, Python's Timsort algorithm is very fast on already-sorted input, so even with a bit of unnecessary sorting, our code is still fast enough.

Upvotes: 0

Nahua Kang
Nahua Kang

Reputation: 406

After deliberately failing an attempt to checkout the complete test input and my output, I found the problem. The line:

teams = sorted(list(set([i[j] for i in countries for j in range(len(i))])))

will make the output problematic in terms of sorting. For example here's a sample input:

10 20 | 43 23 | 27 | 25 | 11 1 12 43 | 33 18 3 43 41 | 31 3 45 4 36 | 25 29 | 1 19 39 | 39 12 16 28 30 37 | 32 | 11 10 7

and it produces the output:

1:5,9; 10:1,12; 11:5,12; 12:5,10; 16:10; 18:6; 19:9; 20:1; 23:2; 25:4,8; 27:3; 28:10; 29:8; 3:6,7; 30:10; 31:7; 32:11; 33:6; 36:7; 37:10; 39:9,10; 4:7; 41:6; 43:2,5,6; 45:7; 7:12;

But the challenge expects the output teams to be sorted by numbers in ascending order, which is not achieved by the above-mentioned code as the numbers are in string format, not integer format. Therefore the solution is simply adding a key to sort the teams list by ascending order for integer:

teams = sorted(list(set([i[j] for i in countries for j in range(len(i))])), key=lambda x:int(x))

With a small change in this line, the code passes through the tests. A sample output looks like:

1:5,9; 3:6,7; 4:7; 7:12; 10:1,12; 11:5,12; 12:5,10; 16:10; 18:6; 19:9; 20:1; 23:2; 25:4,8; 27:3; 28:10; 29:8; 30:10; 31:7; 32:11; 33:6; 36:7; 37:10; 39:9,10; 41:6; 43:2,5,6; 45:7;

Please let me know if you have a better and more efficient solution to the challenge. I'd love to read better codes or great suggestions on improving my programming skills.

Upvotes: 1

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