delete pics to save space

5.24D.cpp

@@ -0,0 +1,46 @@
+#include<cstdio>
+const int maxn=1006;
+int n,m,x,y;
+double f[maxn][maxn],d[maxn][maxn];
+void solve()
+{
+	for(int i=1;i<=m;i++)
+	{
+		double w=1.0/d[i][i];
+		d[i][i]*= w;
+		d[i][m+1]*= w;
+		if(i==m) break;
+		d[i][i+1]*=w;
+		w=d[i+1][i]/d[i][i];
+		d[i+1][i]-=w*d[i][i];
+		d[i+1][i+1]-=w*d[i][i+1];
+		d[i+1][m+1]-=w*d[i][m+1];
+	}
+	for(int i=m-1;i;i--) d[i][m+1]-=d[i+1][m+1]*d[i][i+1];
+}
+int main()
+{
+	#ifdef local
+	freopen("pro.in","r",stdin);
+	#endif
+	scanf("%d%d%d%d",&n,&m,&x,&y);
+	for(int i=n-1;i>=x;i--)
+	{
+		d[1][1]=d[m][m]=-2/3.0;
+		d[1][2]=d[m][m-1]=1/3.0;
+		for(int j=2;j<m;j++)
+		{
+			d[j][m+1]=-f[i+1][j]/4.0-1;
+			d[j][j]=-3/4.0;
+			d[j][j-1]=d[j][j+1]=1/4.0;
+		}
+		if(m==1) d[1][1]=-1/2.0;
+		d[1][m+1]=-f[i+1][1]/3.0-1;
+		d[m][m+1]=-f[i+1][m]/3.0-1;
+		if(m==1) d[m][m+1]=-f[i+1][m]/2.0-1;
+		solve();
+		for(int j=1;j<=m;j++) f[i][j]=d[j][m+1];
+	}
+	printf("%.10f\n",f[x][y]);
+	return 0;
+}