74 lines
2 KiB
Python
74 lines
2 KiB
Python
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""" Implements Multiway number partitioning greedy algorithm """
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import typing as t
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from sortedcontainers import SortedList
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__all__ = ["TaskId", "partition"]
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TaskId = t.NewType("TaskId", int)
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class PartitionException(Exception):
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"""An exception occurring during partitioning"""
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class UnsolvableConflict(PartitionException):
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"""Cannot partition set due to unsolvable conflicts"""
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class Bin:
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"""A bin containing assigned tasks"""
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elts: list[TaskId]
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cost: int
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def __init__(self):
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self.elts = []
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self.cost = 0
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def add(self, task: TaskId, cost: int):
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assert task not in self.elts
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self.elts.append(task)
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self.cost += cost
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def __contains__(self, task: TaskId) -> bool:
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return task in self.elts
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def partition(
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bin_count: int, costs: dict[TaskId, int], multiplicity: dict[TaskId, int]
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) -> list[list[TaskId]]:
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"""Partitions the tasks, each with cost `costs[i]`, into `bin_count` bins. Each
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task has multiplicity `multiplicity[i]`, copies of the same task being mutually
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exclusive (ie. cannot be in the same bin)"""
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bins = SortedList([Bin() for _ in range(bin_count)], key=lambda x: x.cost)
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ordered_tasks: list[TaskId] = []
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for t_id, reps in multiplicity.items():
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for _ in range(reps):
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ordered_tasks.append(t_id)
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ordered_tasks.sort(key=lambda x: costs[x], reverse=True)
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for task in ordered_tasks:
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least_full: Bin
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least_full_pos: int
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for pos, cur_bin in enumerate(bins):
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if task not in cur_bin:
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least_full = cur_bin
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least_full_pos = pos
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break
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else:
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raise UnsolvableConflict(
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"Pas assez de groupes pour affecter la tâche "
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+ f"{task} {multiplicity[task]} fois."
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)
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del bins[least_full_pos]
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least_full.add(task, costs[task])
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bins.add(least_full)
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out: list[list[TaskId]] = []
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for cur_bin in bins:
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out.append(cur_bin.elts)
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return out
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