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# Recursion, generate all pyramid-paths, not working

http://projecteuler.net/index.php?se...problems&id=18
def recur(tree, pos):
if not tree:
return []
else:
return [[tree[0][pos]] + recur(tree[1:], pos)] + \
[[tree[0][pos]] + recur(tree[1:], pos+1)]

i have a list with [[1],[2,3],[4,5,6],[7,8,9,10]]

it i a pyramid so first is 1 then 23 then 456 thrn 78910

from one can go to 2 or 3. from 2 to 4or5, from 3 to 5 or 6.

i want to generate every path and compute the cost.

But I can't get the recursion right. It generates all the paths kind
of but not in a matter i want to.

also having to return after each other doesnt do anything right?
like so:
return [[tree[0][pos]] + recur(tree[1:], pos)]
return [[tree[0][pos]] + recur(tree[1:], pos+1)]

Oct 4 '08 #1
1 1452
process wrote:
http://projecteuler.net/index.php?se...problems&id=18
def recur(tree, pos):
if not tree:
return []
else:
return [[tree[0][pos]] + recur(tree[1:], pos)] + \
[[tree[0][pos]] + recur(tree[1:], pos+1)]
The backslash is not needed here or anytime there is an open (,[,or {.
Note that tree[0][pos] unless -n <= pos < n where n = len(tree)
i have a list with [[1],[2,3],[4,5,6],[7,8,9,10]]

it i a pyramid so first is 1 then 23 then 456 thrn 78910

from one can go to 2 or 3. from 2 to 4or5, from 3 to 5 or 6.

i want to generate every path and compute the cost.

But I can't get the recursion right. It generates all the paths kind
of but not in a matter i want to.
I do not understand what function you are trying to compute from the
verbal description. It is generally best to give a specific example(s)
of what output you expect, as well as what you got.
recur([]) = []

What do you mean by 'kind of' and 'not in a manner I want'? We are not
also having to return after each other doesnt do anything right?
like so:
return [[tree[0][pos]] + recur(tree[1:], pos)]
return [[tree[0][pos]] + recur(tree[1:], pos+1)]
Useless. The second line is never executed.

tjr

Oct 4 '08 #2

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