二分查找

def bin(alist,target):
  i,j=0,len(alist)-1

  while i<=j:
    m = (i+j)//2
    if target == alist[m]:
      return m

    if target > alist[m]:
      i = m+1

    else:
      j = m-1

  return "not found"

if __name__=="__main__":
  alist = [1,2,3,5,8,9]
  target = 5
  index = bin(alist,target)
  print(index)