From 03efb6e64cb3f473a54ee5558952ea4cd826e58e Mon Sep 17 00:00:00 2001
From: Eric Xu <xeric.2002@gmail.com>
Date: Wed, 10 Jul 2024 04:05:10 -0400
Subject: [PATCH] Add BFS solving algorithm

---
 package-lock.json                       |  7 +++++
 package.json                            |  1 +
 src/lib/algorithms/solving/BFS.ts       | 41 +++++++++++++++++++++++++
 src/lib/algorithms/solving/pathUtils.ts | 14 +++++++++
 4 files changed, 63 insertions(+)
 create mode 100644 src/lib/algorithms/solving/BFS.ts
 create mode 100644 src/lib/algorithms/solving/pathUtils.ts

diff --git a/package-lock.json b/package-lock.json
index 240a3d6..1f9cf43 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -8,6 +8,7 @@
       "name": "mazejs",
       "version": "0.1.0",
       "dependencies": {
+        "@datastructures-js/deque": "^1.0.4",
         "async-mutex": "^0.5.0",
         "immer": "^10.1.1",
         "next": "14.2.4",
@@ -532,6 +533,12 @@
         "node": ">=6.9.0"
       }
     },
+    "node_modules/@datastructures-js/deque": {
+      "version": "1.0.4",
+      "resolved": "https://registry.npmjs.org/@datastructures-js/deque/-/deque-1.0.4.tgz",
+      "integrity": "sha512-zlgVSsxqiAd+scLUILvx8E887o+6kYds9/d4DCM/mFOuUITUlPG/r3u5iPZjzW3o6XPPi+p66p3Kf1+wFxYvLQ==",
+      "license": "MIT"
+    },
     "node_modules/@esbuild/aix-ppc64": {
       "version": "0.21.5",
       "resolved": "https://registry.npmjs.org/@esbuild/aix-ppc64/-/aix-ppc64-0.21.5.tgz",
diff --git a/package.json b/package.json
index 285f503..b9682fc 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,7 @@
     "test": "vitest"
   },
   "dependencies": {
+    "@datastructures-js/deque": "^1.0.4",
     "async-mutex": "^0.5.0",
     "immer": "^10.1.1",
     "next": "14.2.4",
diff --git a/src/lib/algorithms/solving/BFS.ts b/src/lib/algorithms/solving/BFS.ts
new file mode 100644
index 0000000..b00d4ba
--- /dev/null
+++ b/src/lib/algorithms/solving/BFS.ts
@@ -0,0 +1,41 @@
+import { MazeCell } from "@/lib/MazeCell";
+import { MazeSolver } from "./MazeSolver";
+import { Deque } from "@datastructures-js/deque";
+import { buildPath } from "./pathUtils";
+
+export class BFS extends MazeSolver {
+  private queue = new Deque<MazeCell>();
+  private cameFrom = new Map<MazeCell, MazeCell>();
+
+  protected _step(): [boolean, Readonly<MazeCell>[]] {
+    const changes: MazeCell[] = [];
+
+    // Go through one queue level
+    const queueSize = this.queue.size();
+    for (let i = 0; i < queueSize; ++i) {
+      const current = this.queue.popFront();
+
+      if (current === this.end) {
+        this._path = buildPath(this.cameFrom, this.end);
+        return [true, []];
+      }
+
+      for (const neighbor of current.connections) {
+        if (neighbor.state === "solid") {
+          neighbor.state = "partial";
+          this.queue.pushBack(neighbor);
+          this.cameFrom.set(neighbor, current);
+          changes.push(neighbor);
+        }
+      }
+    }
+
+    return [this.queue.isEmpty(), changes];
+  }
+
+  protected initialize(): Readonly<MazeCell>[] {
+    this.start.state = "partial";
+    this.queue.pushBack(this.start);
+    return [this.start];
+  }
+}
diff --git a/src/lib/algorithms/solving/pathUtils.ts b/src/lib/algorithms/solving/pathUtils.ts
new file mode 100644
index 0000000..e69b671
--- /dev/null
+++ b/src/lib/algorithms/solving/pathUtils.ts
@@ -0,0 +1,14 @@
+import { MazeCell } from "@/lib/MazeCell";
+
+export function buildPath(
+  cameFrom: Map<MazeCell, MazeCell>,
+  end: MazeCell,
+): MazeCell[] {
+  const path: MazeCell[] = [];
+  let current: MazeCell | null = end;
+  while (current !== null) {
+    path.unshift(current);
+    current = cameFrom.get(current) ?? null;
+  }
+  return path.toReversed();
+}