12. Challenge: Shortest Path

Carla's at a fork in the road and she insists on making the optimal choice for which way to go. This is a classic example of a search problem. In this situation, the optimal path is the shortest path.

Carla has two choices:

  1. Go Left - in which case she will travel a total distance of L3 + L4.

  2. Go Right - in which case she will travel a total distance of L1 + L2.

Complete the function below so that it returns the string L when option 1 is a shorter distance and returns the string R when option 2 is shorter. If the two options are the same it can return either L or R.

Start Quiz:

# Right now the make_decision function ALWAYS decides to go left.
# Modify this function so it behaves appropriately.

def make_decision(L1, L2, L3, L4):
    return "L" 


##########################################################
# 
# The code below is similar to the code that Udacity
# will use to test the correctness of your submission.
# You don't need to modify it but it may
# be helpful to look at for Python syntax help
# 
def test_make_decision():
    # start by initializing this to 0
    number_correct = 0
    
    # TEST 1, should return "R" since right path has 
    # length 5 which is < left path with length 8
    length_1 = 2
    length_2 = 3
    length_3 = 4
    length_4 = 4
    
    decision = make_decision(length_1, length_2, length_3, length_4)
    
    if decision == "R":
        # Test 1 passes
        number_correct = number_correct + 1
        
    # TEST 2, should return "L" since right path still 
    # has length 5 but left is only 3.
    length_3 = 1
    length_4 = 2
    
    decision = make_decision(length_1, length_2, length_3, length_4)
    if decision == "L":
        # Test 2 passes
        number_correct = number_correct + 1
    
    if number_correct == 2:
        all_correct = True
    else:
        all_correct = False
    
    return all_correct
    
if test_make_decision():
    print("Nice work! Your function passed both test cases.")
else:
    print("Not quite. Your function didn't pass both test cases.")

User's Answer:

(Note: The answer done by the user is not guaranteed to be correct)

# Right now the make_decision function ALWAYS decides to go left.
# Modify this function so it behaves appropriately.

def make_decision(L1, L2, L3, L4):
    if (L1 + L2) < (L3 + L4):
        return "R"
    else:
        return "L"


##########################################################
# 
# The code below is similar to the code that Udacity
# will use to test the correctness of your submission.
# You don't need to modify it but it may
# be helpful to look at for Python syntax help
# 
def test_make_decision():
    # start by initializing this to 0
    number_correct = 0
    
    # TEST 1, should return "R" since right path has 
    # length 5 which is < left path with length 8
    length_1 = 2
    length_2 = 3
    length_3 = 4
    length_4 = 4
    
    decision = make_decision(length_1, length_2, length_3, length_4)
    
    if decision == "R":
        # Test 1 passes
        number_correct = number_correct + 1
        
    # TEST 2, should return "L" since right path still 
    # has length 5 but left is only 3.
    length_3 = 1
    length_4 = 2
    
    decision = make_decision(length_1, length_2, length_3, length_4)
    if decision == "L":
        # Test 2 passes
        number_correct = number_correct + 1
    
    if number_correct == 2:
        all_correct = True
    else:
        all_correct = False
    
    return all_correct
    
if test_make_decision():
    print("Nice work! Your function passed both test cases.")
else:
    print("Not quite. Your function didn't pass both test cases.")

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