buffon=function(n, l=0.8, a=1){
  k=0
  theta=runif(n,0,pi); x=runif(n,0,1/2)
  for(t in 1:n){if(x[t]<= l/2*sin(theta[t])) k=k+1 }
  2*l*n/(k*a)
}
buffon(100000,l=0.8,a=1)  # 结果在3.14左右

buf=function(n, l=0.8, a=1){
  k=0
  theta=runif(n,0,pi); x=runif(n,0,1/2)
  for(i in 1:n){ if(x<= 1/2*sin(theta)) k=k+1 }
  2*l*n/(k*a)
}
buf(100000,l=0.8,a=1)   # 结果却在2.51左右