Greedy Fractional Knapsack

fractional_knapsack.py

# Uses python3
import sys

 # returns the ratio of value to weight
def getValueRatio(item):
    return (item[0]/item[1])

def checkInput(n, min, max):
    if n<min or n>max:
        return True
    return False

def getOptimalValue(capacity, weights, values):
    value = 0
    weightCapacity = capacity
    vwRatios = zip(values, weights)
    vwRatiosSorted = sorted(vwRatios, key=getValueRatio, reverse=True)
    for i in vwRatiosSorted:
        iWeight = i[1]
        if weightCapacity == 0:
            return value
        a = min(iWeight, weightCapacity)
        value = value + a * (getValueRatio(i))
        weightCapacity =  weightCapacity - a
    return value

def checkParameters(n, capacity, values, weights):
    # check that n and capacity fit the parameters
    if checkInput(n, 1, 1000):
        sys.exit(0)
    if checkInput(capacity, 0, 2000000):
        sys.exit(0)

    # check that there are enough elements
    if len(values) != n:
        sys.exit(0)
    if len(weights) != n:
        sys.exit(0)

    #check that the values in the arrays fit the parameters
    for i in range(n):
        if checkInput(values[i], 0, 2000000):
            sys.exit(0)
        if checkInput(weights[i], 1, 2000000):
            sys.exit(0)


if __name__ == "__main__":
    data = list(map(int, sys.stdin.read().split()))
    n, capacity = data[0:2]
    values = data[2:(2 * n + 2):2]
    weights = data[3:(2 * n + 2):2]

    checkParameters(n, capacity, values, weights)

    opt_value = getOptimalValue(capacity, weights, values)
    print("{:.10f}".format(opt_value))