google code jam exercise——MilkShakes(2)

继续MilkShakes问题。

之前是使用穷举搜索的方法，能保证结果的准确，但是效率较低，对于large case无法完成测试。后来想用贪心算法来实现。贪心策略是，统计flavor处于malted或unmalted出现的次数，取unmalted出现次数最多的flavor，这样被迫出现的malted的flavor次数会少；取malted出现次数最多的flavor，使得被迫出现malted的次数减少。

在使用贪心算法之前，可以对只有一种选择的customer进行满足，确定一部分flavor。如果不能满足，则直接得到结果。

代码如下：

#!/usr/bin/python
#encoding:UTF-8
#Filename:MilkShakes_Greedy.py

import sys

def preChoice(customers,flavorNum):
    flag = 1
    flavorCnt = flavorNum
    flavorChoice = []
    for i in range(flavorNum):
        flavorChoice.append(-1)

    for customer in customers:
        if customer[0]==1:
            if flavorChoice[customer[1]-1]==-1:
                flavorChoice[customer[1]-1] = customer[2]
            elif flavorChoice[customer[1]-1]!=customer[2]:
                flag = 0
                break
            flavorCnt = flavorCnt - 1

    return [flag,flavorCnt,flavorChoice]


def statistic(customers,choice):
    flavorMalted = []
    flavorUnMalted = []
    for i in range(flavorNum):
        flavorMalted.append(0)
        flavorUnMalted.append(0)

    flag = 0
    for customer in customers:
        for i in range(customer[0]):
            j = 2 * i + 1
            if choice[customer[j]-1] == customer[j+1]:
                flag = 1
                break
                #continue
        if flag!=1:
            for i in range(customer[0]):
                j = 2 * i + 1
                if customer[j+1]==1:
                    flavorMalted[customer[j]-1] = flavorMalted[customer[j]-1] + 1
                else:
                    flavorUnMalted[customer[j]-1] = flavorUnMalted[customer[j]-1] + 1

    return [flavorMalted, flavorUnMalted]

def maxi(flavor):
    m = max(flavor)
    for i,v in enumerate(flavor):
        if v==m:
            return [i,v]


inname = "input.txt"
outname = "output.txt"
if len(sys.argv)>1:
    inname = sys.argv[1]
    outname = inname.rstrip(".in")
    outname = outname + ".out"
fin = open(inname,"r")
fout = open(outname,"w")

line = fin.readline()

testCaseNum = int(line)

caseNum = 0

for caseNum in range(testCaseNum):
    line = fin.readline()
    flavorNum = int(line)
    line = fin.readline()
    customerNum = int(line)
#    lines = fin.readlines(customerNum)
    customers = []
#    for line in lines:
#    print "Case #%d:" %(caseNum+1)
#    print flavorNum
#    print customerNum
    for i in range(customerNum):
        line = fin.readline()
        line = line.rstrip("\n")
        customer = [int(val) for val in line.split()]
#        print customer
        customers.append(customer)

#    print "\n"

    answer = "Case #%d:" %(caseNum+1)
    tpre = preChoice(customers,flavorNum)

#    print tpre

    flag = tpre[0]
    if flag ==0:
        answer = answer + " IMPOSSIBLE"
    else:
        flavorCnt = tpre[1]
        flavorChoice = tpre[2]
        while(1):
#            print flavorChoice
            stat = statistic(customers,flavorChoice)
            flavorM = stat[0]
            flavorU = stat[1]
            for i in range(flavorNum):
                if flavorChoice[i]!=-1:
                    flavorM[i] = 0
                    flavorU[i] = 0
#            print "M:"        
#            print flavorM
#            print "U:"
#            print flavorU

            mm = maxi(flavorM)
            mu = maxi(flavorU)
            if mm[1]==0:
                for i in range(flavorNum):
                    if flavorChoice[i]==-1:
                        flavorChoice[i]=0
                flag = 1
                break
            elif mu[1]==0:
                for i in range(flavorNum):
                    if flavorChoice[i]==-1:
                        flavorChoice[i]=1
                flag = 1
                break
            else:
                if mm[0]==mu[0]:
                    if mm[1]>mu[1]:
                        flavorChoice[mm[0]] = 1
                    else:
                        flavorChoice[mm[0]] = 0
                else:
                    flavorChoice[mu[0]] = 0

                flavorCnt = flavorCnt - 1
                
                if flavorCnt==0:
                    if mm[1]>0 or mu[1]>0:
                        flag = 0
                    break

        if flag==1:
            for val in flavorChoice:
                answer = answer + " " + str(val)
        else:
            answer = answer + " IMPOSSIBLE"

    answer = answer + "\n"
        
    fout.write(answer)

fin.close()
fout.close()

    

对该程序进行测试，small case和large case都可以得到结果，不过没有百分之百的正确。

small case测试结果中，有6个结果不一致，总数是100个。large case没有标准答案，提交测试显示不正确，但不知道有多少不正确。

前面的贪心策略有些混乱，接下来继续整理。