Snake and ladder problem.

Author: deepakhb2

Interview-Questions/snake_n_ladder.rb

@@ -0,0 +1,63 @@
+=begin
+
+Rules The game is played with a cubic die of  faces numbered  to .
+
+Starting from square , land on square  with the exact roll of the die. If moving the number rolled would place the player beyond square , no move is made.
+
+If a player lands at the base of a ladder, the player must climb the ladder. Ladders go up only.
+
+If a player lands at the mouth of a snake, the player must go down the snake and come out through the tail. Snakes go down only.
+
+Input: 
+3
+32 62
+42 68
+12 98
+7
+95 13
+97 25
+93 37
+79 27
+75 19
+49 47
+67 17
+
+=end
+
+def quickest_way_up(ladders, snakes)
+  h_snakes, h_ladders = {}, {}
+  ladders.each do |ladder|
+    h_ladders[ladder[0]] = ladder[1]
+  end
+  snakes.each do |snake|
+    h_snakes[snake[0]] = snake[1]
+  end
+  adj_nodes = {}
+  (0...100).each do |node|
+    (node+1..node+6).each do |i|
+      next_pos = h_ladders[i] || h_snakes[i] || i 
+      if(adj_nodes[node])
+        adj_nodes[node] << next_pos if next_pos <= 100
+      else
+        adj_nodes[node] = [next_pos]
+      end
+    end
+  end
+  dist = {1 => 0}
+  queue = [1]
+  while(!queue.empty?)
+    c_node = queue.shift
+    adj_nodes[c_node].each do |neigh|
+      if(!dist[neigh])
+        queue.push(neigh) if neigh < 100
+        dist[neigh] = dist[c_node] + 1
+        return dist[neigh] if neigh == 100
+      end
+    end
+  end
+  return -1
+end
+
+ladders = [[32,62], [42, 68], [12, 98]]
+snakes = [[95, 13], [97, 25], [93, 37], [79, 27], [75, 19], [49, 47], [67, 17]]
+p quickest_way_up(ladders, snakes)