p<-c(.1,.2,.3,.3,.1) 	#P(X=0), P(X=1), etc
sum(p)			#check
cp<-c(0,cumsum(p))
nsim<-5000
X<-array(0,c(nsim,1))
for(i in 1:nsim)
{
	u<-runif(1)
	X[i]<-sum(cp<u)-1
}
hist(X)