#----------------------------------------------------------------------
# BUILDING LISTS
#
# Copyright (C) September 22, 2017 -- Dr. William T. Verts
#
# Start with an empty list
# run a for-loop the right number of times, and for each pass through the loop:
#     add a [thing] to the end of the list (may be dependent on loop control variable)
#----------------------------------------------------------------------

#----------------------------------------------------------------------
# Build a list of the squares of all integers from 0 through 19
#----------------------------------------------------------------------

def Example1():
    L = []
    for I in range(20):
        L = L + [I*I]
    return L
    
#----------------------------------------------------------------------
# Build a list of 5 numeric values entered by the user
# (the str function changes its argument into a string)
#----------------------------------------------------------------------

def Example2():
    L = []
    for I in range(5):
        L = L + [input(str(I) + " Enter a number: ")]
    return L

#----------------------------------------------------------------------
# Build a list of squares of the integers from the given list
# (for-loops don't necessarily have to use ranges)
#----------------------------------------------------------------------

def Example3():
    L = []
    for I in [3, -4, 1, 6, 0]:
        L = L + [I*I]
    return L
    
#----------------------------------------------------------------------
# Build a list of the squares of all even numbers between 0 and 19
# (The % operator, mod, means "compute the remainder of a division",
# and the double-equal == is used to compare two values for equality)
#----------------------------------------------------------------------

def Example4():
    L = []
    for I in range(20):
        if ((I % 2) == 0):              # True only if I is even
            L = L + [I*I]
    return L
    
#----------------------------------------------------------------------
# Build the same list as in #4, but use range to avoid needing the if 
#----------------------------------------------------------------------

def Example5():
    L = []
    for I in range(0,20,2):
        L = L + [I*I]
    return L
    
#----------------------------------------------------------------------
# Build a list of 25 zeroes [0,0,0,0,...,0,0]
# (The item added to the list need not involve the loop variable I at
# all.   Note that this can also be done as L = [0] * 25)
#----------------------------------------------------------------------

def Example6():
    L = []
    for I in range(25):
        L = L + [0]
    return L
    
#----------------------------------------------------------------------
# LIST COMPREHENSIONS
#
# All of the earlier functions can be done with a single line statement
# called a "list comprehension", which embeds the list constructor,
# computed expression, for-loop, and optionally an if-statement, into
# a single statement.
#----------------------------------------------------------------------

L1 = [I*I for I in range(20)]                                   # Example #1
L2 = [input(str(I) + " Enter a number: ") for I in range(5)]    # Example #2
L3 = [I*I for I in [3, -4, 1, 6, 0]]                            # Example #3
L4 = [I*I for I in range(20) if ((I % 2) == 0)]                 # Example #4
L5 = [I*I for I in range(0,20,2)]                               # Example #5
L6 = [0 for I in range(25)]                                     # Example #6

print "L1 = ", L1
print "L2 = ", L2
print "L3 = ", L3
print "L4 = ", L4
print "L5 = ", L5
print "L6 = ", L6

#----------------------------------------------------------------------
# Compute the Hailstone list for positive integer N (this was
# assignment #1 from last Spring).  If N is even, divide it by 2.
# If N is odd, multiply it by 3 and add 1.  Do this as long as N
# is greater than 1.  Return all computed values.
# Hailstone1 was presented in class; Hailstone2 is a variation.
# This is the kind of program you will do in the first assignment.
#----------------------------------------------------------------------

def Hailstone1(N):      # N is a positive integer
    L = []
    while (N > 1):
        L = L + [N]
        if ((N % 2) == 1):
            N = N * 3 + 1
        else:
            N = N / 2
    L = L + [1]
    return L
    
def Hailstone2(N):      # N is a positive integer
    L = [N]
    while (N > 1):
        if ((N % 2) == 1):
            N = N * 3 + 1
        else:
            N = N / 2
        L = L + [N]
    return L