Improve day 24

day24/common/blizzard.go

@@ -22,6 +22,7 @@ type Map struct {
   height int
   width int
   cache [][][]int
+  bestDistance int
 }
 
 func (tileMap *Map) InitCache() {
@@ -35,6 +36,7 @@ func (tileMap *Map) InitCache() {
       }
     }
   }
+  tileMap.bestDistance = math.MaxInt32
 }
 
 func (tileMap *Map) GetDistanceToEnd(currentSteps int) int {
@@ -48,8 +50,6 @@ func (tileMap *Map) GetDistanceToEnd(currentSteps int) int {
       break
     }
   }
-  tileMap.cache[startSteps][0][startCol] = currentSteps
-  tileMap.PropagateDistanceFromTile(startSteps, startCol, 0, currentSteps)
 
   endCol := 0
   for i := 0; i < tileMap.width; i++ {
@@ -59,13 +59,10 @@ func (tileMap *Map) GetDistanceToEnd(currentSteps int) int {
     }
   }
 
-  minDistance := math.MaxInt32
-  for i := 0; i < tileMap.steps; i++ {
-    if tileMap.cache[i][len(tileMap.tiles[0])-1][endCol] < minDistance {
-      minDistance = tileMap.cache[i][len(tileMap.tiles[0])-1][endCol]
-    }
-  }
-  return minDistance
+  tileMap.cache[startSteps][0][startCol] = currentSteps
+  tileMap.PropagateDistanceFromTile(startSteps, startCol, 0, currentSteps, endCol, len(tileMap.tiles[startSteps])-1)
+
+  return tileMap.bestDistance
 }
 
 func (tileMap *Map) GetDistanceToStart(currentSteps int) int {
@@ -79,8 +76,6 @@ func (tileMap *Map) GetDistanceToStart(currentSteps int) int {
       break
     }
   }
-  tileMap.cache[startSteps][len(tileMap.tiles[startSteps])-1][endCol] = currentSteps
-  tileMap.PropagateDistanceFromTile(startSteps, endCol, len(tileMap.tiles[startSteps])-1, currentSteps)
 
   startCol := 0
   for i := 0; i < tileMap.width; i++ {
@@ -90,37 +85,61 @@ func (tileMap *Map) GetDistanceToStart(currentSteps int) int {
     }
   }
 
-  minDistance := math.MaxInt32
-  for i := 0; i < tileMap.steps; i++ {
-    if tileMap.cache[i][0][startCol] < minDistance {
-      minDistance = tileMap.cache[i][0][startCol]
-    }
-  }
-  return minDistance
+  tileMap.cache[startSteps][len(tileMap.tiles[startSteps])-1][endCol] = currentSteps
+  tileMap.PropagateDistanceFromTile(startSteps, endCol, len(tileMap.tiles[startSteps])-1, currentSteps, startCol, 0)
+
+  return tileMap.bestDistance
 }
 
-func (tileMap *Map) PropagateDistanceFromTile(step, x, y, currentDistance int) {
+func (tileMap *Map) PropagateDistanceFromTile(step, x, y, currentDistance, targetX, targetY int) {
   nextStep := (step + 1) % tileMap.steps
+  orders := []byte{0, 1, 2, 3, 4}
+  distances := []int{(x-targetX)*(x-targetX)+(y+1-targetY)*(y+1-targetY),
+                     (x+1-targetX)*(x+1-targetX)+(y-targetY)*(y-targetY),
+                     (x-targetX)*(x-targetX)+(y-targetY)*(y-targetY),
+                     (x-1-targetX)*(x-1-targetX)+(y-targetY)*(y-targetY),
+                     (x-targetX)*(x-targetX)+(y-1-targetY)*(y-1-targetY)}
 
-  if x > 0 && tileMap.tiles[nextStep][y][x-1] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y][x-1] {
-    tileMap.cache[nextStep][y][x-1] = currentDistance + 1
-    tileMap.PropagateDistanceFromTile(nextStep, x-1, y, currentDistance+1)
+  if currentDistance >= tileMap.bestDistance {
+    return
   }
-  if x < tileMap.width - 1 && tileMap.tiles[nextStep][y][x+1] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y][x+1] {
-    tileMap.cache[nextStep][y][x+1] = currentDistance + 1
-    tileMap.PropagateDistanceFromTile(nextStep, x+1, y, currentDistance+1)
+
+  if x == targetX && y == targetY {
+    tileMap.bestDistance = currentDistance
   }
-  if y > 0 && tileMap.tiles[nextStep][y-1][x] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y-1][x] {
-    tileMap.cache[nextStep][y-1][x] = currentDistance + 1
-    tileMap.PropagateDistanceFromTile(nextStep, x, y-1, currentDistance+1)
+
+  sorted := false
+  for !sorted {
+    sorted = true
+    for i := 0; i < 4; i++ {
+      if distances[orders[i]] > distances[orders[i+1]] {
+        orders[i], orders[i+1] = orders[i+1], orders[i]
+        sorted = false
+      }
+    }
   }
-  if y < tileMap.height - 1 && tileMap.tiles[nextStep][y+1][x] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y+1][x] {
-    tileMap.cache[nextStep][y+1][x] = currentDistance + 1
-    tileMap.PropagateDistanceFromTile(nextStep, x, y+1, currentDistance+1)
-  }
-  if tileMap.tiles[nextStep][y][x] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y][x] {
-    tileMap.cache[nextStep][y][x] = currentDistance + 1
-    tileMap.PropagateDistanceFromTile(nextStep, x, y, currentDistance+1)
+
+  for _, order := range orders {
+    if order == 0 && y < tileMap.height - 1 && tileMap.tiles[nextStep][y+1][x] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y+1][x] {
+      tileMap.cache[nextStep][y+1][x] = currentDistance + 1
+      tileMap.PropagateDistanceFromTile(nextStep, x, y+1, currentDistance+1, targetX, targetY)
+    }
+    if order == 1 && x < tileMap.width - 1 && tileMap.tiles[nextStep][y][x+1] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y][x+1] {
+      tileMap.cache[nextStep][y][x+1] = currentDistance + 1
+      tileMap.PropagateDistanceFromTile(nextStep, x+1, y, currentDistance+1, targetX, targetY)
+    }
+    if order == 2 && tileMap.tiles[nextStep][y][x] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y][x] {
+      tileMap.cache[nextStep][y][x] = currentDistance + 1
+      tileMap.PropagateDistanceFromTile(nextStep, x, y, currentDistance+1, targetX, targetY)
+    }
+    if order == 3 && x > 0 && tileMap.tiles[nextStep][y][x-1] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y][x-1] {
+      tileMap.cache[nextStep][y][x-1] = currentDistance + 1
+      tileMap.PropagateDistanceFromTile(nextStep, x-1, y, currentDistance+1, targetX, targetY)
+    }
+    if order == 4 && y > 0 && tileMap.tiles[nextStep][y-1][x] == Empty && currentDistance + 1 < tileMap.cache[nextStep][y-1][x] {
+      tileMap.cache[nextStep][y-1][x] = currentDistance + 1
+      tileMap.PropagateDistanceFromTile(nextStep, x, y-1, currentDistance+1, targetX, targetY)
+    }
   }
 }