Recursive targeting clear solution for Berserk Rook by DiZ - python coding challenges

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Recursive targeting solution in Clear category for Berserk Rook by DiZ

def berserk_rook(berserker, enemies):
    #Target set construction
    left = set()
    for i,c in enumerate(map(ord, berserker)):              ##On the same row/column:
        for o in 0,8:                                       ##For each side:
            for r in map(chr, range(c-8+o, c+o)):                 ##Search the
                target = ''.join(([r]+list(berserker)+[r])[i::2]) ##closest rook
                if target in enemies:                             ##and
                    left.add(target)                              ##target it.
                    break
    #Search through remaining enemies
    return len(left)and 1+max(berserk_rook(enemy, enemies-{enemy}) for enemy in left)

Aug. 1, 2014

Comments:

ArchTauruS on Sept. 24, 2014, 7:51 a.m.
I think this algorithm is cool, but it's hard to me to understand.

DiZ on Sept. 24, 2014, 9:33 a.m.
Don't hesitate to ask for clarification if necessary ;)

thibault.dereu on Jan. 19, 2016, 7:58 p.m.
I think this solution is not correct. Your rook captures the first enemy in the row or in the column, jumping over other enemies between. berserk_rook('d3', {'a3','b1','b2','b3'}) should return 3, not 4.

DiZ on Jan. 22, 2016, 2:48 p.m.
It seems you're wrong. What if I capture towers in this order: a3, b3, b2, b1?

thibault.dereu on Jan. 22, 2016, 9:08 p.m.
The rook starts from position d3. It cannot capture a3 first because it would have to jump over b3, which is not allowed.

DiZ on Jan. 23, 2016, 10:09 p.m.
You're not wrong but this mission is not about traditional chess. It doesn't prevent you to jump over another enemy. Think of it as a loophole in the mission description.

thibault.dereu on Jan. 24, 2016, 2:55 p.m.
The mission description does state that the "rook may not leap over other pieces".

DiZ on Jan. 25, 2016, 8:43 a.m.
I made a corrected version available <a href="http://www.checkio.org/mission/berserk-rook/publications/DiZ/python-3/good-recursive/">here</a> Quick fix on two lines: <pre class='brush: python'>for o in -1,1: for r in map(chr, range(c, c+8*o, o)): </pre> I also took this opportunity to make an optimization: <pre class='brush: python'>target = (r+berserker+r)[i::2] </pre> Much quicker on 4 characters than this ugly join! You can also make a pull request to correct the test cases and invalidate this solution (and many others).

Different kind of sets

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