12. 挑战：最短路径

Carla 正位于一个岔路口，她坚持要做出 最佳 选择，选择最好的路径。 这是一个 搜索 问题的典型例子。在这种情况下，最佳路径是 最短 路径。

Carla 有两个选择：

1.往左走 - 在这种情况下，她将行驶的总路程为 L3 + L4。

2.往右走 - 在这种情况下，她将行驶的总路程为 L1 + L2。

完成下面的函数，当选项 1 较短时，返回字符串 “L”，当选项 2 较短时，返回字符串 “R”。如果两个选项相同，则可能返回 “L” 或 “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.")

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