This array is for dynamic programming.
You can diagonalize it into a list and use technique similar to the
Fibonacci numbers.
The resulting solution should be purely declarative.
2012/12/11 mukesh tiwari
Hello All I am trying to transform this C++ code in Haskell. In case any one interested this is solution of SPOJ problem.
#include<cstdio> #include<iostream> #include<cstring> using namespace std;
int memo[1100][1100] ;
int recurse( int h , int a , int cnt , bool flag ) { if ( h <= 0 || a <= 0 ) return cnt ; if ( memo[h][a] ) return memo[h][a] ; if ( flag ) memo[h][a] = recurse ( h + 3 , a + 2 , cnt + 1 , !flag ) ; else memo[h][a] = max ( memo[h][a] , max ( recurse ( h - 5 , a - 10 , cnt + 1 , !flag ) , recurse ( h - 20 , a + 5 , cnt + 1 , !flag ) ) ) ;
return memo[h][a]; }
int main() { int n , a , b ; scanf( "%d", &n ); for(int i = 0 ; i < n ; i++) { memset ( memo , 0 , sizeof memo ) ; scanf("%d%d", &a , &b ); printf("%d\n" , recurse( a , b , -1 , 1 )); if( i != ( n - 1 ) ) printf("\n"); }
}
I am stuck with that memo[1100][1100] is global variable so I tried to solve this problem using state monad ( Don't know if its correct approach or not ) but it certainly does not seem correct to me. Till now I came up with code. Could some one please tell me how to solve this kind of problem ( Generally we have a global variable either multi dimensional array or map and we store the best values found so far in the table ).
import qualified Data.Map.Strict as SM import Control.Monad.State
{-- funsolve_WF :: Int -> Int -> Int -> Int funsolve_WF h a cnt | h <= 0 || a <= 0 = cnt | otherwise = funsolve_Air h a ( cnt + 1 )
funsolve_Air :: Int -> Int -> Int -> Int funsolve_Air h a cnt = max ( funsolve_WF ( h + 3 - 5 ) ( a + 2 - 10 ) cnt' ) ( funsolve_WF ( h + 3 - 20 ) ( a + 2 + 5 ) cnt' ) where cnt' = cnt + 1 --}
funSolve :: Int -> Int -> Int -> Bool -> State ( SM.Map ( Int , Int ) Int ) Int funSolve hl am cnt f | hl <= 0 && am <= 0 = return cnt | otherwise = do mp <- get case () of _| SM.member ( hl , am ) mp -> return mp SM.! ( hl , am ) | f -> do --here I have to insert the value return by function funSolve ( hl + 3 ) ( am + 2 ) ( cnt + 1 ) ( not f ) to map whose key is ( hl , am ) let k = evalState ( funSolve ( hl + 3 ) ( am + 2 ) ( cnt + 1 ) ( not f ) ) mp modify ( SM.insert ( hl , am ) k )
| otherwise -> do do let k_1 = evalState ( funSolve ( hl - 5 ) ( am - 10 ) ( cnt + 1 ) ( not f ) ) mp k_2 = evalState ( funSolve ( hl - 20 ) ( am + 5 ) ( cnt + 1 ) ( not f ) ) mp k_3 = mp SM.! ( hl , am ) modify ( SM.insert ( hl , am ) ( maximum [ k_1 , k_2 , k_3 ] ) )
Regards Mukesh Tiwari
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