From 942c61da33976c5e847985d9fb50eb836d97a014 Mon Sep 17 00:00:00 2001
From: Kabul Totakhil <totakhilkamran7@gmail.com>
Date: Tue, 3 Jun 2025 12:08:25 -0700
Subject: [PATCH] complete the bfs livecode

---
 src/Search.java | 147 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 125 insertions(+), 22 deletions(-)

diff --git a/src/Search.java b/src/Search.java
index cebb278..ff9b9bc 100644
--- a/src/Search.java
+++ b/src/Search.java
@@ -1,34 +1,137 @@
+import java.util.LinkedList;
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Queue;
+
 public class Search {
-     /**
+
+    /**
      * Finds the location of the nearest reachable cheese from the rat's position.
-     * Returns a 2-element int array: [row, col] of the closest 'c'. If there are multiple
-     * cheeses that are tied for the same shortest distance to reach, return
-     * any one of them.
-     * 
+     * Returns a 2‐element int array: [row, col] of the closest 'c'. If there are multiple
+     * cheeses tied for the same shortest distance, returns any one of them.
+     *
      * 'R' - the rat's starting position (exactly one)
      * 'o' - open space the rat can walk on
      * 'w' - wall the rat cannot pass through
      * 'c' - cheese that the rat wants to reach
-     * 
+     *
      * If no rat is found, throws EscapedRatException.
      * If more than one rat is found, throws CrowdedMazeException.
-     * If no cheese is reachable, throws HungryRatException
+     * If no cheese is reachable, throws HungryRatException.
      *
-     * oooocwco
-     * woowwcwo
-     * ooooRwoo
-     * oowwwooo
-     * oooocooo
+     * Example maze:
+     *   oooocwco
+     *   woowwcwo
+     *   ooooRwoo
+     *   oowwwooo
+     *   oooocooo
      *
-     * The method will return [0,4] as the nearest cheese.
-     *
-     * @param maze 2D char array representing the maze
-     * @return int[] location of the closest cheese in row, column format
-     * @throws EscapedRatException if there is no rat in the maze
-     * @throws CrowdedMazeException if there is more than one rat in the maze
-     * @throws HungryRatException if there is no reachable cheese
+     * The method will return [0, 4] as the nearest cheese.
+     */
+    public static int[] nearestCheese(char[][] maze)
+            throws EscapedRatException, CrowdedMazeException, HungryRatException {
+
+        // 1) Find the rat's starting location (and check exception conditions)
+        int[] start = ratLocation(maze);
+
+        // 2) Prepare a visited array
+        boolean[][] visited = new boolean[maze.length][maze[0].length];
+
+        // 3) Standard BFS queue of (row,col) pairs
+        Queue<int[]> queue = new LinkedList<>();
+        queue.add(start);
+
+        while (!queue.isEmpty()) {
+            int[] current = queue.poll();
+            int curR = current[0];
+            int curC = current[1];
+
+            // Skip if already visited
+            if (visited[curR][curC]) {
+                continue;
+            }
+            visited[curR][curC] = true;
+
+            // If this cell is cheese, we found the nearest cheese
+            if (maze[curR][curC] == 'c') {
+                return new int[] { curR, curC };
+            }
+
+            // Otherwise, enqueue all valid neighbors
+            for (int[] neighbor : getNeighbors(maze, current)) {
+                int nr = neighbor[0], nc = neighbor[1];
+                if (!visited[nr][nc]) {
+                    queue.add(neighbor);
+                }
+            }
+        }
+
+        // If BFS completes without finding any cheese, the rat is hungry
+        throw new HungryRatException();
+    }
+
+
+    /**
+     * Returns a list of valid neighbor positions (up/down/left/right)
+     * that the rat can move into from the current cell. A neighbor is valid if:
+     *   - It stays inside the maze bounds
+     *   - It is not a wall ('w')
+     */
+    public static List<int[]> getNeighbors(char[][] maze, int[] current) {
+        int curR = current[0];
+        int curC = current[1];
+        List<int[]> neighbors = new ArrayList<>();
+
+        // Define the four possible directions: up, down, left, right.
+        int[][] directions = {
+            { -1, 0 }, // up
+            {  1, 0 }, // down
+            {  0, -1}, // left
+            {  0, 1 }  // right
+        };
+
+        for (int[] dir : directions) {
+            int newR = curR + dir[0];
+            int newC = curC + dir[1];
+
+            // Check bounds
+            if (newR >= 0 && newR < maze.length && newC >= 0 && newC < maze[0].length) {
+                // Only walkable if not a wall
+                if (maze[newR][newC] != 'w') {
+                    neighbors.add(new int[] { newR, newC });
+                }
+            }
+        }
+        return neighbors;
+    }
+
+
+    /**
+     * Scans the entire maze to find the rat ('R'). If no rat is present, throws EscapedRatException.
+     * If more than one 'R' is present, throws CrowdedMazeException. Otherwise returns the [row, col].
      */
-    public static int[] nearestCheese(char[][] maze) throws EscapedRatException, CrowdedMazeException, HungryRatException {
-        return null;
+    public static int[] ratLocation(char[][] maze)
+            throws EscapedRatException, CrowdedMazeException {
+
+        int[] location = null;
+
+        for (int r = 0; r < maze.length; r++) {
+            for (int c = 0; c < maze[0].length; c++) {
+                if (maze[r][c] == 'R') {
+                    if (location != null) {
+                        // We already found one rat before → too many rats
+                        throw new CrowdedMazeException();
+                    }
+                    location = new int[] { r, c };
+                }
+            }
+        }
+
+        if (location == null) {
+            // No 'R' found
+            throw new EscapedRatException();
+        }
+
+        return location;
     }
-}
\ No newline at end of file
+}