From e40c41ddfb5adfdd5bd12bee0829b479c7524264 Mon Sep 17 00:00:00 2001
From: Karma Riuk <riukkarma@gmail.com>
Date: Tue, 15 Aug 2023 18:43:18 +0200
Subject: [PATCH] feat: implemented a* algorithm

---
 solver/a-star.go | 66 ++++++++++++++++++++++++++++++++++++++++++++++++
 solver/solver.go |  4 +++
 2 files changed, 70 insertions(+)
 create mode 100644 solver/a-star.go

diff --git a/solver/a-star.go b/solver/a-star.go
new file mode 100644
index 0000000..f4922b0
--- /dev/null
+++ b/solver/a-star.go
@@ -0,0 +1,66 @@
+package solver
+
+import (
+	"maze-solver/maze"
+	"maze-solver/utils"
+	"sort"
+)
+
+type AStarSolver struct {
+	dist_from_start map[*maze.Node]int
+	dist_from_end   map[*maze.Node]int
+	parent          map[*maze.Node]*maze.Node
+	stack           sorted_stack
+}
+
+func (s *AStarSolver) Solve(m *maze.Maze) *maze.SolvedMaze {
+	defer utils.Timer("A* algorithm", 2)()
+	s.dist_from_start = make(map[*maze.Node]int, len(m.Nodes))
+	s.dist_from_end = make(map[*maze.Node]int, len(m.Nodes))
+	s.parent = make(map[*maze.Node]*maze.Node, len(m.Nodes))
+
+	current, end := m.Nodes[0], m.Nodes[len(m.Nodes)-1]
+
+	for _, node := range m.Nodes {
+		s.dist_from_start[node] = 0
+		s.dist_from_end[node] = int(node.Coords.Distance(end.Coords))
+	}
+
+	for current != end {
+		current.Visited = true
+
+		for _, child := range []*maze.Node{current.Left, current.Right, current.Up, current.Down} {
+			if child != nil {
+				dist := s.dist_from_start[current] + int(current.Coords.Distance(child.Coords))
+				if !child.Visited {
+					s.parent[child] = current
+					s.dist_from_start[child] = dist
+					s.stack.insert(child, &s.dist_from_end)
+				} else if s.dist_from_start[child] > dist {
+					s.parent[child] = current
+					s.dist_from_start[child] = dist
+					sort.Slice(s.stack, func(i, j int) bool {
+						return s.dist_from_end[s.stack[i]] < s.dist_from_end[s.stack[j]]
+					})
+				}
+			}
+		}
+		current = s.stack.pop()
+	}
+
+	solution := make([]*maze.Node, 0, len(m.Nodes))
+	for current != m.Nodes[0] {
+		solution = append(solution, current)
+		current = s.parent[current]
+	}
+	solution = append(solution, m.Nodes[0])
+
+	for i, j := 0, len(solution)-1; i < j; i, j = i+1, j-1 {
+		solution[i], solution[j] = solution[j], solution[i]
+	}
+
+	return &maze.SolvedMaze{
+		Maze:     m,
+		Solution: solution,
+	}
+}
diff --git a/solver/solver.go b/solver/solver.go
index bb985c4..1a735ed 100644
--- a/solver/solver.go
+++ b/solver/solver.go
@@ -17,12 +17,14 @@ const (
 	_DFS      = "dfs"
 	_BFS      = "bfs"
 	_Dijkstra = "dijkstra"
+	_AStar    = "a-star"
 )
 
 var TYPES = []string{
 	_DFS,
 	_BFS,
 	_Dijkstra,
+	_AStar,
 }
 
 func (f *SolverFactory) Get() Solver {
@@ -31,6 +33,8 @@ func (f *SolverFactory) Get() Solver {
 		return &DFSSolver{}
 	case _BFS:
 		return &BFSSolver{}
+	case _AStar:
+		return &AStarSolver{}
 	case _Dijkstra:
 		return &DijkstraSolver{}
 	}