1. mystery.py
2. search_compare.py
3. twod_exercises.py

# Practice with 2D lists
# by Sara Sprenkle

def main():
    matrix = createMatrix()
    print("Before:")
    print(matrix)
    mystery(matrix)
    print("After:")
    print(matrix)

def mystery(a):
    """ "run" this on A, at right """
    for row in range( len(a) ):
        for col in range( len(a[0]) ):
            if row == col:
                a[row][col] = 42
            else:
                a[row][col] += 1

def createMatrix():
    a0 = list(range(1,5))
    a1 = list(range(5,9))
    a2 = list(range(9,13))
    a = []
    a.append(a0)
    a.append(a1)
    a.append(a2)
    return a

main()

# Compare the linear and binary searching techniques by the number of
# comparisons.
# by Sara Sprenkle

def main():

    print("This program helps us to empirically compare search strategies.")
    print("Metric: Number of comparisons required to find the key.")
    print("\nDisclaimer: May not be a completely fair comparison but gives us an idea.")
    print()

    # The keys I want to search for in a list
    #keys = [1, 4, 13, 19, 125, 126, 127]
    keys = [1, 4, 13, 19, 125, 126, 127, 19997, 19998, 19999]

    NUM_ENTRIES = 10000
    
    # the list of integers that I'm searching (odd numbers)
    integers = list(range(1,NUM_ENTRIES*2,2))
    print("Creating list of size", NUM_ENTRIES, "starting at 1 and incrementing by 2 to", NUM_ENTRIES*2)
    print()
    
    print("KEY is the number we're looking for.\n")

    print("%6s|%14s" % ("","# Comparisons"))
    print("%6s| %6s %6s" % ("KEY", "LIN", "BIN"))
    print("-"* 24)
    
    total_lin_comp = 0.0
    total_bin_comp = 0.0
    
    for key in keys:
        lin_comp = linearSearch(integers,key)
        bin_comp = binarySearch(integers,key)
        print("%6d| %6d %6d" % (key, lin_comp, bin_comp))
        
        # update the total number of comparisons
        total_lin_comp += lin_comp
        total_bin_comp += bin_comp
    
    print()
    print("ON AVERAGE...")
    print("-"*50)
    print()
    print("The average number of comparisons per search for")
    print("\tlinear search was", total_lin_comp/len(keys))
    print("\tbinary search was", total_bin_comp/len(keys))


# Return the number of comparisons required to find the key.
def linearSearch(searchlist, key):
    numChecks = 0
    for elem in searchlist:
        numChecks += 1
        if elem == key:
            return numChecks
    return numChecks

# Return the number of comparisons required to find the key
def binarySearch(searchlist, key):
    low = 0
    high = len(searchlist)-1
    numChecks = 0
    while low <= high:
        mid = (low+high)//2
        numChecks+= 2  # while comparison, next if comparison
        if searchlist[mid] == key:
            return numChecks
        numChecks+=1
        if searchlist[mid] < key:
            low = mid+1
        else:
            high = mid-1
    return numChecks

main()

# Practice with 2D Lists
# Sara Sprenkle

def main():
    #rows = int(input("How many rows? "))
    #columns = int(input("How many columns? "))

    rows = 3
    columns = 4

    print()
    print("Correct Matrix Creation:")
    print('-'*30)
    matrix = create2DList(rows, columns)
    print(matrix)

    print("\nAssigning matrix[1][2]=3")
    matrix[1][2] = 3
    print("Result: ")
    print(matrix)

    print()
    print("*"*55)
    print("Incorrect Matrix Creation:")
    print('-'*30)

    matrix = noCreate2DList(rows, columns)
    print(matrix)

    print("\nAssigning matrix[1][2]=3")
    print("Result: ")
    matrix[1][2] = 3
    print(matrix)


def create2DList(rows, cols):
    """Returns a two-dimensional list filled with 0s that is 'rows' tall and
    'cols' wide."""
    twodlist = []
    for rowPos in range(rows):
        # creates a new list
        row = []
        for colPos in range(cols):
            row.append(0)
        twodlist.append(row)
    return twodlist

def noCreate2DList(rows, cols):
    """Does not create a 2D list because each 'row' points to the same list in
    memory."""
    
    twodlist = []
    # creates one list
    onerow = []
    for colPos in range(cols):
        onerow.append(0)
    for rowPos in range(rows):
        twodlist.append(onerow)
        
    return twodlist
    

main()