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knapsack_1.py
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knapsack_1.py
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#! /usr/bin/env python3
# -*- coding: utf-8 -*-
import sys;
import time;
import functools;
class Instance:
def __init__(self):
self.Id = 0;
self.N = 0;
self.M = 0;
self.Items = [];
def solve(self, method, cycles):
if 'bruteforce' == method:
return self.__solve_bruteforce(cycles);
elif 'heuristic' == method:
return self.__solve_heuristic(cycles);
else:
raise Exception("Unknown solving method: {}".format(method));
def __solve_bruteforce(self, cycles):
start = time.clock();
for cycle in range(0, cycles):
best_cost = 0;
for combination in range(0, 2 ** self.N):
cost = 0;
weight = 0;
bitmask = 1;
for i in range(0, self.N):
if 0 != (combination & bitmask):
cost += self.Items[i].Cost;
weight += self.Items[i].Weight;
bitmask <<= 1;
if weight <= self.M and cost > best_cost:
best_cost = cost;
end = time.clock();
running_time = (end - start) / cycles;
return (best_cost, running_time);
def __solve_heuristic(self, cycles):
start = time.clock();
for cycle in range(0, cycles):
cost = 0;
weight = 0;
sorted_items = sorted(self.Items, key = functools.cmp_to_key(lambda item1, item2: item1.Cost / item1.Weight >= item2.Cost / item2.Weight));
for i in sorted_items:
if weight + i.Weight <= self.M:
cost += i.Cost
weight += i.Weight
end = time.clock();
running_time = (end - start) / cycles;
return (cost, running_time);
class Item:
def __init__(self):
self.Weight = 0;
self.Cost = 0;
def main(argc, argv):
if 2 > argc:
print("Usage: {} <instances> [<cycles>]\n".format(argv[0]));
return 1;
cycles = 1
if 3 == argc:
cycles = int(argv[2])
instances = [];
with open(argv[1], mode = "r") as f:
for l in f:
line_splitted = l.split(' ');
new_instance = Instance();
new_instance.Id = int(line_splitted[0]);
new_instance.N = int(line_splitted[1]);
new_instance.M = int(line_splitted[2]);
for i in range(3, len(line_splitted), 2):
new_item = Item();
new_item.Weight = int(line_splitted[i + 0]);
new_item.Cost = int(line_splitted[i + 1]);
new_instance.Items.append(new_item);
instances.append(new_instance);
f.close();
exact_result = {}
for method in ["bruteforce", "heuristic"]:
total_runtime = 0
average_runtime = 0
total_relative_error = 0
maximum_relative_error = 0
average_relative_error = 0
for instance in instances:
print("Solving instance {} using {}... ".format(instance.Id, method), end='');
result = instance.solve(method, 4096 if 'heuristic' == method else cycles);
print("Result: {:8}, Time: {:24.16f}.".format(result[0], result[1]));
total_runtime += result[1]
if 'bruteforce' == method:
exact_result[instance] = result;
elif 'heuristic' == method:
relative_error = abs(result[0] - exact_result[instance][0]) / exact_result[instance][0];
total_relative_error += relative_error;
maximum_relative_error = max(maximum_relative_error, relative_error);
average_runtime = total_runtime / len(instances);
print("Total runtime: {:24.16f}, average runtime: {:24.16f}.".format(total_runtime, average_runtime));
if 'heuristic' == method:
average_relative_error = total_relative_error / len(instances);
print("Maximum relative error: {:.8f}, average relative error: {:.8f}.".format(maximum_relative_error, average_relative_error));
return 0;
if "__main__" == __name__:
sys.exit(main(len(sys.argv), sys.argv));