recursively implementing 'minimum number of coins' in python

Question

This problem is same as asked in here.

Given a list of coins, their values (c1, c2, c3, ... cj, ...), and the total sum i. Find the minimum number of coins the sum

Answer 1

Like the comment says, you need to return a big enough value when i < 0, so that it won't get selected by your min like this:

cdict = {}
def C(i, coins):

    if i == 0:
        return 0

   if i < 0:
        return 1e100    # Return infinity in ideally

    if i in cdict:
        return cdict[i]
    else:
        answer = 1 + min([C(i - cj, coins) for cj in coins])
        cdict[i] = answer
    return answer

now whenever the function returns 1e100, it means solution is not possible.

for example:

$ python2 coins.py 13555 1 5 9
1507  coins
$ python2 coins.py 139 1 5 9
19  coins
$ python2 coins.py 139  5 9
19  coins
$ python2 coins.py 13977  5 9
1553  coins
$ python2 coins.py 13977   9
1553  coins
$ python2 coins.py 139772   9
1e+100  coins

with usage:

python2 coins.py    ...