help with a DP problem.

Revision en2, by kofhearts, 2015-12-14 06:14:07

hello codeforces,

I have come here to ask help to dp experts. I will highly appreciate it if you can help solve this dilemma. I have been struggling with this for a while now.

THe problem can be found here.

http://codeforces.me/contest/69/problem/D

Now i am not working on a general solution. My algorithm is just for the first test case and i am confused why the result is "Anton loses" when the correct answer is "Anton wins". I have stepped through the logic of my DP formulation and i dont seem to spot the fallacy. So, can you please point out the point where my logic fails. I will highly appreciate it. Thanks for your time. I have commented out parts of my code for legibility.


import math #For the following test case #0 0 2 3 #1 1 #1 2 # # #x --> x coordinate #y --> y coordinate #t --> if t == True then Anton turn, if t == False then Dasha turn #fs --> if first player or Anton has swapped, since only 1 swap is possible #ss --> if second player or Dasha has swapped, since only 1 swap is possible def canWin(x, y, t, fs, ss): if math.sqrt(float(x)*float(x) + float(y)*float(y)) > 3: return False if t == False and ss == False: #if Dasha turn and if dasha hasnt swapped then can swap 1 time return (not (canWin(x + 1, y + 1, not t, fs, ss))) and (not canWin(x + 1, y + 2, not t, fs, ss)) and (not canWin(y, x, not t, fs, True)) elif t == True and fs == False: #if Anton turn and if Anton hasnt swapped then can swap 1 time return (not (canWin(x + 1, y + 1, not t, fs, ss))) and (not canWin(x + 1, y + 2, not t, fs, ss)) and (not canWin(y, x, not t, True, ss)) else: #since both has swapped 1 time now cannot swap further return (not (canWin(x + 1, y + 1, not t, fs, ss))) and (not canWin(x + 1, y + 2, not t, fs, ss)) print canWin(0, 0, True, False, False) #Expected result was True since Anton wins but the result is False

Also, please note that i have removed the memoization part for now as to make the code short and easy to understand so i guess this is not a dp solution. But i am just trying to find the fallacy in my recurrence formula. Thanks!

Tags factorisation

History

 
 
 
 
Revisions
 
 
  Rev. Lang. By When Δ Comment
en5 English kofhearts 2015-12-18 11:48:03 1070
en4 English kofhearts 2015-12-14 17:18:49 2111 solved
en3 English kofhearts 2015-12-14 07:05:45 1465 added full code
en2 English kofhearts 2015-12-14 06:14:07 228 added a clarification
en1 English kofhearts 2015-12-14 06:06:59 1978 Initial revision (published)