How to get solution path from greedy algorithm?

Question

I have greedy algoithm with job scheduling problem, but I want to return which one projects were chosen to get this max value, how can I do that?

from dataclasses import dataclass
from datetime import date


@dataclass
class InvestmentProject:
    profit: int
    begin_date: date
    end_date: date


def get_max_sequence(arr, i=0):
    if i == len(arr):
        return 0
    j = i + 1
    while j < len(arr) and arr[i].end_date > arr[j].begin_date:
        j += 1
    one = arr[i].profit + get_max_sequence(arr, j)
    two = get_max_sequence(arr, i+1)
    return max(one, two)


def main():
    arr = [
        InvestmentProject(30, date(2022, 10, 10), date(2022, 10, 14)),
        InvestmentProject(15, date(2022, 10, 15), date(2022, 10, 16)),
        InvestmentProject(25, date(2022, 10, 12), date(2022, 10, 15)),
        InvestmentProject(10, date(2022, 10, 20), date(2022, 10, 26)),
    ]
    print(get_max_sequence(sorted(arr, key=lambda x: x.begin_date)))

Asked By: Reboot

||

Source

Answer 1

You could always return value and list of indexes.

First

if i == len(arr):
   return 0, []

Next you would have to always get value and list before calculations

    val, indexes = get_max_sequence(arr, j)

    one = arr[i].profit + val
    
    two, other_indexes = get_max_sequence(arr, i+1)

And you would have to manually check max()

    if one > two:
        return one, indexes + [i]
    else:
        return two, other_indexes

Minimal working code:

from dataclasses import dataclass
from datetime import date


@dataclass
class InvestmentProject:
    profit: int
    begin_date: date
    end_date: date


def get_max_sequence(arr, i=0):
    if i == len(arr):
        return 0, []
    
    j = i + 1
    while j < len(arr) and arr[i].end_date > arr[j].begin_date:
        j += 1
        
    val, indexes = get_max_sequence(arr, j)
    one = arr[i].profit + val
    
    two, other_indexes = get_max_sequence(arr, i+1)
    
    if one > two:
        print('one:', indexes+[i])
        return one, indexes + [i]
    else:
        print('two:', other_indexes)
        return two, other_indexes


def main():
    arr = [
        InvestmentProject(30, date(2022, 10, 10), date(2022, 10, 14)),
        InvestmentProject(15, date(2022, 10, 15), date(2022, 10, 16)),
        InvestmentProject(25, date(2022, 10, 12), date(2022, 10, 15)),
        InvestmentProject(10, date(2022, 10, 20), date(2022, 10, 26)),
    ]
    
    arr = list(sorted(arr, key=lambda x: x.begin_date))
    for item in arr:
        print(item)
    print(get_max_sequence(arr))
    
main()

Answered By: furas

How to get solution path from greedy algorithm?

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