18.py

L = """75
95 64
17 47 82
18 35 87 10
20 04 82 47 65
19 01 23 75 03 34
88 02 77 73 07 63 67
99 65 04 28 06 16 70 92
41 41 26 56 83 40 80 70 33
41 48 72 33 47 32 37 16 94 29
53 71 44 65 25 43 91 52 97 51 14
70 11 33 28 77 73 17 78 39 68 17 57
91 71 52 38 17 14 91 43 58 50 27 29 48
63 66 04 68 89 53 67 30 73 16 69 87 40 31
04 62 98 27 23 09 70 98 73 93 38 53 60 04 23""".split("\n")
L = [map(lambda x: int(x), l.split()) for l in L]
M = [[0 for _ in range(len(l))] for l in L]
M[0][0] = L[0][0]
M[1][0] = L[0][0] + L[1][0]
M[1][1] = L[0][0] + L[1][1]

path = [L[0][0]]
j = 0
for i in range(2, len(L)):
    for j in range(len(L[i])):
        if 0 < j < len(L[i]) - 1:
            M[i][j] = L[i][j] + max(M[i-1][j], M[i-1][j-1])
        elif j==0:
            M[i][j] = L[i][j] + M[i-1][j]
        else:
            M[i][j] = L[i][j] + M[i-1][j-1]
print max(M[-1])