Index: src/game.d
==================================================================
--- src/game.d
+++ src/game.d
@@ -144,10 +144,11 @@
 		this.tr_source = cast(Pos[][char])m.tr_source;
 		this.hige = m.hige.clone();
 		this.razor = m.razor;
 		this.collected_lambda = m.collected_lambda;
 		this.total_lambda = m.total_lambda;
+		this.may_update = (cast(Map)m).may_update.dup;
 	}
 
 	this(string[] raw_data, string[string] params, char[char] trampo)
 	{
 		int width = 0;
@@ -165,10 +166,12 @@
 				this.robot = new Pos(y,x);
 			if(this[y,x] == 'L' || this[y,x] == 'O')
 				this.lift = new Pos(y,x);
 			if(this[y,x] == '\\' || this[y,x] == '@')
 				total_lambda++;
+			if(this[y,x] == '*' || this[y,x] == '@')
+				may_update ~= new Pos(y,x);
 		}
 
 		Pos[char] tr_pos;
 		for(int y=1; y<=H; ++y)
 		for(int x=1; x<=W; ++x) {
@@ -268,13 +271,22 @@
 
 		return update(turn);
 	}
 
 	bool rocky(char c) { return c=='*' || c=='@'; }
+	Pos[] may_update;
+		void emptified(Pos p) {
+			for(int dy=0; dy<=+1; ++dy)
+			for(int dx=-1; dx<=+1; ++dx)
+				may_update ~= new Pos(p.y+dy, p.x+dx);
+		}
 
 	bool move(int dy, int dx, int turn)
 	{
+
+		emptified(robot);
+
 		int y = robot.y;
 		int x = robot.x;
 		if( '\\' == this[y+dy,x+dx] )
 			collected_lambda++;
 		if( '!' == this[y+dy,x+dx] )
@@ -290,65 +302,74 @@
 			this[y+dy*2,x+dx*2]=rock;
 			robot = new Pos(y+dy,x+dx);
 		} else if('A'<=this[y+dy,x+dx] && this[y+dy,x+dx]<='I') {
 			this[y,x]=' ';
 			Pos tp = tr_target[this[y+dy,x+dx]];
-			foreach(p; tr_source[this[tp]])
+			foreach(p; tr_source[this[tp]]) {
+				emptified(p);
 				this[p] = ' ';
+			}
 			this[tp] = 'R';
 			robot = tp;
 		}
 		return update(turn);
 	}
 
 	bool update(int turn)
 	{
+		// Write after all the updates are processed.
+		Tuple!(int,int,char)[] write_buffer;
+		void write(int y, int x, char c) { write_buffer ~= tuple(y,x,c); }
+		void writep(Pos p, char c) { write_buffer ~= tuple(0+p.y,0+p.x,c); }
+		scope(exit) {
+			may_update.length = 0;
+			foreach(wr; write_buffer) {
+				this[wr[0],wr[1]] = wr[2];
+				if(rocky(wr[2]))
+					may_update ~= new Pos(wr[0],wr[1]);
+				if(wr[2]==' ')
+					emptified(new Pos(wr[0], wr[1]));
+			}
+		}
+
+		if(collected_lambda == total_lambda)
+			if(this[lift]=='L')
+				this[lift] = 'O';
+
 		bool dead = false;
-
-		char[][] next;
-		foreach(y,s; data)
-			next ~= s.dup;
-
-		ref char access(Pos p) { return next[H-p.y][p.x-1]; }
-
-		for(int y=1; y<=H; ++y)
-		for(int x=1; x<=W; ++x) {
-			Pos p = new Pos(y,x);
+		sort(may_update);
+		foreach(p; may_update) {
+			int y = p.y, x = p.x;
 			char rock = this[p];
 			if(rocky(this[p])) {
 				if(this[p.D]==' ') {
-					access(p)  =' ';
-					access(p.D)=(rock=='@'&&this[p.D.D]!=' ' ? '\\' : rock);
+					writep(p, ' ');
+					writep(p.D, (rock=='@'&&this[p.D.D]!=' ' ? '\\' : rock));
 					if(robot == p.D.D)
 						dead=true;
 				}
 				else if((rocky(this[p.D]) || this[p.D]=='\\') && this[p.R]==' ' && this[p.R.D]==' ') {
-					access(p)=' ';
-					access(p.R.D)=(rock=='@'&&this[p.R.D.D]!=' ' ? '\\' : rock);
+					writep(p, ' ');
+					writep(p.R.D,(rock=='@'&&this[p.R.D.D]!=' ' ? '\\' : rock));
 					if(robot == p.R.D.D)
 						dead=true;
 				}
 				else if(rocky(this[p.D]) && this[p.L]==' ' && this[p.L.D]==' ') {
-					access(p)=' ';
-					access(p.L.D)=(rock=='@'&&this[p.L.D.D]!=' ' ? '\\' : rock);
+					writep(p, ' ');
+					writep(p.L.D, (rock=='@'&&this[p.L.D.D]!=' ' ? '\\' : rock));
 					if(robot == p.L.D.D)
 						dead=true;
 				}
 			}
-			else if(this[p]=='L') {
-				if(collected_lambda == total_lambda)
-					access(p) = 'O';
-			}
 			else if(this[p]=='W') {
 				if( hige.is_growing_turn(turn) )
 					for(int dy=-1; dy<=+1; ++dy)
 					for(int dx=-1; dx<=+1; ++dx)
 						if(this[p.y+dy,p.x+dx] == ' ')
-							access(new Pos(p.y+dy,p.x+dx)) = 'W';
+							write(p.y+dy,p.x+dx,'W');
 			}
 		}
-		data = next;
 		return dead;
 	}
 }
 
 ////////////////////////////////////////////////////////////////////////////////

Index: src/solver.d
==================================================================
--- src/solver.d
+++ src/solver.d
@@ -387,8 +387,8 @@
 		else
 			plan = plan[1..$];
 	}
 }
 
-//alias Solver_2!(Solver_1) MainSolver;
+alias Solver_2!(Solver_1) MainSolver;
 //alias Solver_1 MainSolver;
-alias Solver_0 MainSolver;
+//alias Solver_0 MainSolver;