MIT6_0002F16_lec1.pdf

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An objective function that is to be maximized or
minimized, e.g.,
J Minimize time spent traveling from New York to Boston
A set of constraints (possibly empty) that must be
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J Cannot spend more than $100
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class Food(object):
def __init__(self, n, v, w):
self.name = n
self.value = v
self.calories = w
def getValue(self):
return self.value
def getCost(self):
return self.calories
def density(self):
return self.getValue()/self.getCost()
def __str__(self):
return self.name + ': ' + str(self.value)
+ ', ' + str(self.calories) + ''
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+ $+%%%)
def buildMenu(names, values, calories):
names, values, calories lists of same length.
name a list of strings
values and calories lists of numbers
returns list of Foods
menu = []
for i in range(len(values)):
menu.append(Food(names[i], values[i],
calories[i]))
return menu
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def greedy(items, maxCost, keyFunction):
Assumes items a list, maxCost = 0,
keyFunction maps elements of items to numbers
itemsCopy = sorted(items, key = keyFunction,
reverse = True)
result = []
totalValue, totalCost = 0.0, 0.0
for i in range(len(itemsCopy)):
if (totalCost+itemsCopy[i].getCost()) = maxCost:
result.append(itemsCopy[i])
totalCost += itemsCopy[i].getCost()
totalValue += itemsCopy[i].getValue()
return (result, totalValue)
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def greedy(items, maxCost, keyFunction):
itemsCopy = sorted(items, key = keyFunction,
reverse = True)
result = []
totalValue, totalCost = 0.0, 0.0
for i in range(len(itemsCopy)):
if (totalCost+itemsCopy[i].getCost()) = maxCost:
result.append(itemsCopy[i])
totalCost += itemsCopy[i].getCost()
totalValue += itemsCopy[i].getValue()
return (result, totalValue)
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) $(/
def testGreedy(items, constraint, keyFunction):
taken, val = greedy(items, constraint, keyFunction)
print('Total value of items taken =', val)
for item in taken:
print(' ', item)
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) $(/
def testGreedys(maxUnits):
print('Use greedy by value to allocate', maxUnits,
'calories')
testGreedy(foods, maxUnits, Food.getValue)
print('nUse greedy by cost to allocate', maxUnits,
'calories')
testGreedy(foods, maxUnits,
lambda x: 1/Food.getCost(x))
print('nUse greedy by density to allocate', maxUnits,
'calories')
testGreedy(foods, maxUnits, Food.density)
testGreedys(800)
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) $(/
def testGreedys(foods, maxUnits):
print('Use greedy by value to allocate', maxUnits,
'calories')
testGreedy(foods, maxUnits, Food.getValue)
print('nUse greedy by cost to allocate', maxUnits,
'calories')
testGreedy(foods, maxUnits,
lambda x: 1/Food.getCost(x))
print('nUse greedy by density to allocate', maxUnits,
'calories')
testGreedy(foods, maxUnits, Food.density)
names = ['wine', 'beer', 'pizza', 'burger', 'fries',
'cola', 'apple', 'donut', 'cake']
values = [89,90,95,100,90,79,50,10]
calories = [123,154,258,354,365,150,95,195]
foods = buildMenu(names, values, calories)
testGreedys(foods, 750)
)#
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MIT OpenCourseWare
https://ocw.mit.edu
6.0002 Introduction to Computational Thinking and Data Science
Fall 2016
For information about citing these materials or our Terms of Use, visit: https://ocw.mit.edu/terms.

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