CS412-Applied-Algorithms/Greedy-Algorithms/cs412_knapsack_fractional.py

"""
name:  Nicholas Tamassia

Honor Code and Acknowledgments:

        This work complies with the JMU Honor Code.

       Comments here on your code and submission.
"""

from dataclasses import dataclass
from typing import override


# I don't like tuples
@dataclass(frozen=True)
class KnapsackItem:
    name: str
    value: float
    weight: float

    @property
    def value_per(self) -> float:
        return self.value / self.weight

    @override
    def __str__(self) -> str:
        return f"{self.name}({self.value:.2f}, {self.weight:.2f})"

    @staticmethod
    def from_str(string: str) -> "KnapsackItem":
        values: list[str] = string.split()
        name, value, weight = values[0], float(values[1]), float(values[2])
        return KnapsackItem(name, value, weight)


def knapsack(
    capacity: int, items: list[KnapsackItem]
) -> tuple[list[KnapsackItem], float]:
    cur_capacity: float = capacity
    sorted_items: list[KnapsackItem] = sorted(items, key=lambda i: -i.value_per)

    total_value: float = 0.0
    fractional_items: list[KnapsackItem] = []

    for item in sorted_items:
        if abs(cur_capacity) < 1e-8:
            break

        if cur_capacity < item.weight:
            value: float = item.value_per * cur_capacity
            total_value += value
            fractional_items.append(KnapsackItem(item.name, value, cur_capacity))
            cur_capacity = 0
        else:
            total_value += item.value
            fractional_items.append(KnapsackItem(item.name, item.value, item.weight))
            cur_capacity -= item.weight

    return fractional_items, total_value


# All modules for CS 412 must include a main method that allows it
# to imported and invoked from other python scripts
def main():
    capacity: int = int(input())
    n: int = int(input())

    items: list[KnapsackItem] = [KnapsackItem.from_str(input()) for _ in range(0, n)]

    fractional_items, total_value = knapsack(capacity, items)

    print(" ".join(map(str, fractional_items)))
    print(total_value)


if __name__ == "__main__":
    main()