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A knapsack Le Monde mathematical puzzle:

Given n packages weighting each at most 5.8kg for a total weight of 300kg, is it always possible to allocate these packages  to 12 separate boxes weighting at most 30kg each? weighting at most 29kg each?

This can be checked by brute force using the following R code

#generate packages
paca=runif(1,0,5.8)
while (sum(paca)<300){
paca=c(paca,runif(1,0,5.8))}
paca=paca[-length(paca)]
paca=c(paca,300-sum(paca))


and

#check if they can be partitioned into
#12 groups of weight less than 30
box=vector(mode="list",length=12)
#random allocation
alloc=sample(1:12,length(paca),rep=TRUE)
content=rep(0,12)
for (i in 1:12){
box[[i]]=paca[alloc==i]
content[i]=sum(box[[i]])}
content=content*(content>0)
#wrong allocation
while (max(content)>30){
i=sample(1:12,1,prob=content)
j=sample(1:length(box[[i]]),1,prob=box[[i]])
#reallocation
k=sample(1:12,1,prob=max(content)-content)
while (k==i){
k=sample(1:12,1,prob=max(content)-content)}
content[i]=content[i]-box[[i]][j]
content[i]=content[i]*(content[i]>0)
content[k]=content[k]+box[[i]][j]
box[[k]]=c(box[[k]],box[[i]][j])
box[[i]]=box[[i]][-j]}


repeatedly and could not find an endless while loop. (Empty boxes sometimes lead to negative contents, hence my fix setting negative contents to zero.) But neither did I find an issue when the upper bound on the weight is 29kg… So it is either possible or rarely impossible! The R code immediately gets stuck when setting the bound at 25kg.

Filed under: Books, Kids, R Tagged: knapsack problem, Le Monde, mathematical puzzle, R