tvl-depot/scratch/facebook/knapsack-faq.py

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from utils import get, init_table, print_table
# This problem has a few variants:
# - limited supply of each item
# - unlimited supply of each item
# - fractional amounts of each item (e.g. rice)
def max_haul(capacity, items):
min_kg = min([kg for _, kg in items])
max_kg = max([kg for _, kg in items])
cols = int(max_kg / min_kg)
fr_col_index = lambda index: min_kg * index + min_kg
to_col_index = lambda capacity: int((capacity - min_kg) * cols / max_kg)
table = init_table(rows=len(items), cols=cols, default=0)
for row in range(len(table)):
for col in range(len(table[row])):
curr_capacity = fr_col_index(col)
value, kg = items[row]
if kg > curr_capacity:
a = 0
else:
a = value + get(table, row - 1, to_col_index(curr_capacity - kg))
b = get(table, row - 1, col)
table[row][col] = max([a, b])
print_table(table)
return table[-1][-1]
guitar = (1500, 1)
stereo = (3000, 4)
laptop = (2000, 3)
necklace = (2000, 0.5)
items = [necklace, guitar, stereo, laptop]
capacity = 4
result = max_haul(capacity, items)
expected = 4000
print(result, expected)
assert result == expected
print("Success!")