From 8becddb3cef76fe0cccb140770b4fc75beefed34 Mon Sep 17 00:00:00 2001
From: Pierre Jeanjean <rhiobet@gmail.com>
Date: Mon, 12 Dec 2022 09:20:14 +0100
Subject: [PATCH] Day 12

---
 day12/common/heightmap.go | 142 ++++++++++++++++++++++++++++++++++++++
 day12/ex1/main.go         |  16 +++++
 day12/ex2/main.go         |  16 +++++
 3 files changed, 174 insertions(+)
 create mode 100644 day12/common/heightmap.go
 create mode 100644 day12/ex1/main.go
 create mode 100644 day12/ex2/main.go

diff --git a/day12/common/heightmap.go b/day12/common/heightmap.go
new file mode 100644
index 0000000..d6d22e2
--- /dev/null
+++ b/day12/common/heightmap.go
@@ -0,0 +1,142 @@
+package common
+
+import (
+	"bufio"
+	"math"
+)
+
+
+type Tile struct {
+  height int
+  steps int
+}
+
+func NewTile(height int) *Tile {
+  return &Tile{height, math.MaxInt32}
+}
+
+func (tile Tile) GetSteps() int {
+  return tile.steps
+}
+
+
+type Map struct {
+  tiles [][]Tile
+  start *Tile
+  end *Tile
+}
+
+func (heightmap Map) GetEndTile() Tile {
+  return *heightmap.end
+}
+
+func (heightmap Map) GetStartTile() Tile {
+  return *heightmap.start
+}
+
+func (heightmap Map) FindBestStart() Tile {
+  min := math.MaxInt32
+  var bestStart Tile
+  for i := 0; i < len(heightmap.tiles); i++ {
+    for j := 0; j < len(heightmap.tiles[i]); j++ {
+      if heightmap.tiles[i][j].height == 1 && heightmap.tiles[i][j].steps < min {
+        bestStart = heightmap.tiles[i][j]
+        min = bestStart.steps
+      }
+    }
+  }
+  return bestStart
+}
+
+func (heightmap *Map) ComputeStepsFromStart() {
+  heightmap.start.steps = 0
+  for i := 0; i < len(heightmap.tiles); i++ {
+    for j := 0; j < len(heightmap.tiles[i]); j++ {
+      if &heightmap.tiles[i][j] == heightmap.start {
+        heightmap.ComputeSteps(i, j, 1)
+      }
+    }
+  }
+}
+
+func (heightmap *Map) ComputeStepsFromEnd() {
+  heightmap.end.steps = 0
+  for i := 0; i < len(heightmap.tiles); i++ {
+    for j := 0; j < len(heightmap.tiles[i]); j++ {
+      if &heightmap.tiles[i][j] == heightmap.end {
+        heightmap.ComputeStepsInReverse(i, j, 1)
+      }
+    }
+  }
+}
+
+func (heightmap *Map) ComputeSteps(row int, column int, steps int) {
+  if row > 0 && heightmap.tiles[row-1][column].steps > steps &&
+          heightmap.tiles[row-1][column].height <= heightmap.tiles[row][column].height + 1 {
+    heightmap.tiles[row-1][column].steps = steps
+    heightmap.ComputeSteps(row-1, column, steps+1)
+  }
+  if row < len(heightmap.tiles)-1 && heightmap.tiles[row+1][column].steps > steps &&
+          heightmap.tiles[row+1][column].height <= heightmap.tiles[row][column].height + 1 {
+    heightmap.tiles[row+1][column].steps = steps
+    heightmap.ComputeSteps(row+1, column, steps+1)
+  }
+  if column > 0 && heightmap.tiles[row][column-1].steps > steps &&
+          heightmap.tiles[row][column-1].height <= heightmap.tiles[row][column].height + 1 {
+    heightmap.tiles[row][column-1].steps = steps
+    heightmap.ComputeSteps(row, column-1, steps+1)
+  }
+  if column < len(heightmap.tiles[0])-1 && heightmap.tiles[row][column+1].steps > steps &&
+          heightmap.tiles[row][column+1].height <= heightmap.tiles[row][column].height + 1 {
+    heightmap.tiles[row][column+1].steps = steps
+    heightmap.ComputeSteps(row, column+1, steps+1)
+  }
+}
+
+func (heightmap *Map) ComputeStepsInReverse(row int, column int, steps int) {
+  if row > 0 && heightmap.tiles[row-1][column].steps > steps &&
+          heightmap.tiles[row-1][column].height + 1 >= heightmap.tiles[row][column].height {
+    heightmap.tiles[row-1][column].steps = steps
+    heightmap.ComputeStepsInReverse(row-1, column, steps+1)
+  }
+  if row < len(heightmap.tiles)-1 && heightmap.tiles[row+1][column].steps > steps &&
+          heightmap.tiles[row+1][column].height + 1 >= heightmap.tiles[row][column].height {
+    heightmap.tiles[row+1][column].steps = steps
+    heightmap.ComputeStepsInReverse(row+1, column, steps+1)
+  }
+  if column > 0 && heightmap.tiles[row][column-1].steps > steps &&
+          heightmap.tiles[row][column-1].height + 1 >= heightmap.tiles[row][column].height {
+    heightmap.tiles[row][column-1].steps = steps
+    heightmap.ComputeStepsInReverse(row, column-1, steps+1)
+  }
+  if column < len(heightmap.tiles[0])-1 && heightmap.tiles[row][column+1].steps > steps &&
+          heightmap.tiles[row][column+1].height + 1 >= heightmap.tiles[row][column].height {
+    heightmap.tiles[row][column+1].steps = steps
+    heightmap.ComputeStepsInReverse(row, column+1, steps+1)
+  }
+}
+
+
+func Parse(scanner bufio.Scanner) Map {
+  heightmap := Map{}
+
+  for scanner.Scan() {
+    line := scanner.Text()
+
+    heightmapRow := make([]Tile, len(line))
+    for i := 0; i < len(line); i++ {
+      if line[i] == 'S' {
+        heightmapRow[i] = *NewTile(1)
+        heightmap.start = &heightmapRow[i]
+      } else if line[i] == 'E' {
+        heightmapRow[i] = *NewTile(26)
+        heightmap.end = &heightmapRow[i]
+      } else {
+        heightmapRow[i] = *NewTile(int(line[i] - 'a' + 1))
+      }
+    }
+    heightmap.tiles = append(heightmap.tiles, heightmapRow)
+  }
+
+  return heightmap
+}
diff --git a/day12/ex1/main.go b/day12/ex1/main.go
new file mode 100644
index 0000000..e26e34e
--- /dev/null
+++ b/day12/ex1/main.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"aoc2022/day12/common"
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+  heightmap := common.Parse(*bufio.NewScanner(os.Stdin))
+
+  heightmap.ComputeStepsFromStart()
+
+  fmt.Println(heightmap.GetEndTile().GetSteps())
+}
diff --git a/day12/ex2/main.go b/day12/ex2/main.go
new file mode 100644
index 0000000..69c354f
--- /dev/null
+++ b/day12/ex2/main.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"aoc2022/day12/common"
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+  heightmap := common.Parse(*bufio.NewScanner(os.Stdin))
+
+  heightmap.ComputeStepsFromEnd()
+
+  fmt.Println(heightmap.FindBestStart().GetSteps())
+}