Wikioi 1010

1010.c

/* Wikioi - Problem 1010 Dabing crossing the river. */
#include <stdio.h>

#define CONTROLEDBYHORSE(i, j)	( (X == (i) && Y == (j)) || (X-1 == (i) && Y-2 == (j)) || (X-2 == (i) && Y-1 == (j)) || (X-2 == (i) && Y+1 == (j)) || (X-1 == (i) && Y+2 == (j)) || (X+1 == (i) && Y-2 == (j)) || (X+2 == (i) && Y-1 == (j)) || (X+2 == (i) && Y+1 == (j)) || (X+1 == (i) && Y+2 == (j)) )
#define OUTOFBOARD(i, j)		( ((i) > n) || ((j) > m) )

typedef long long int lint;

int n = 0, m = 0;
int X = 0, Y = 0;

lint dp_v[21][21] = {{0}};
lint dp(int i, int j)
{
	lint *ans = &(dp_v[i][j]);
	
	if( *ans )
		return *ans;
	if( OUTOFBOARD(i,j) || CONTROLEDBYHORSE(i,j) )
		return 0;
	if( n == i && m == j )
		return 1;
	return ( *ans = dp(i+1,j) + dp(i,j+1) );
}


int
main(void)
{
	scanf("%d %d %d %d", &n, &m, &X, &Y);
	printf("%lld\n", dp(0,0));
	return 0;
}