"""File:     bin_srch_tst.py
   Purpose:  Compare the run-time of binary search and linear search
             of a list of ints

   Run:      python bin_srch_tst.py

   Input:    The number of ints in the list.  The number of values to
             search for.
   Output:   The average time it took to search the list using
             binary and linear search.
"""
from random import randint
from time import time

def bin_srch(l, min, max, val):
   """See if val belongs to l between subscript min and subscript max"""
   if (min <= max):
      mid = (min+max)/2
      if val == l[mid]:
         return mid
      elif val < l[mid]:
         return bin_srch(l, min, mid-1, val)
      else: # val > l[mid]
         return bin_srch(l, mid+1, max, val)
   else: # min > max.  val not in list
      return None

#----------------------------------------------------------------------
def lin_srch(l, val):
   """Use linear search to try to find val in l"""
   for i in xrange(len(l)):
      if l[i] == val:
         return i
   return None

#----------------------------------------------------------------------
def gen_list(l, n, max):
   """Generate a list of n random ints"""
   for i in xrange(n):
      l.append(randint(0,max))

#----------------------------------------------------------------------
# Main program
n = int(raw_input("How many elements in the list?\n   "))
srch_count = int(raw_input("How many elements should we search for?\n   "))

l = []
gen_list(l, n, 2*n)
l.sort()
#print "l =", l

srch_vals = []
gen_list(srch_vals, srch_count, n)
#print "srch_vals =", srch_vals

start = time()
for i in xrange(srch_count):
   loc = bin_srch(l, 0, n-1, srch_vals[i])
#  print "bin_srch: ", srch_vals[i], "in loc", loc
finish = time()
bin_srch_time = finish-start;
print "Average time for binary search =", bin_srch_time/srch_count, "seconds"

start = time()
for i in xrange(srch_count):
   loc = lin_srch(l, srch_vals[i])
#  print "lin_srch: ", srch_vals[i], "in loc", loc
finish = time()
lin_srch_time = finish-start;
print "Average time for linear search =", lin_srch_time/srch_count, "seconds"