Java Code that finds the shortest path in a matrix from point A to point B

static List<Integer> minSeen = new ArrayList<Integer>();
 public static void main (String[] args) throws java.lang.Exception
 {
  Scanner sc = new Scanner(System.in);
  int t = sc.nextInt();
  for(int i=0;i<t;i++) {
      int n = sc.nextInt();
      int m = sc.nextInt();
      char[][] arr = new char[n][m];
      sc.nextLine();
      int startI = -1;
      int startJ = -1;
      for(int j=0;j<n;j++) {
          int count=0;
          String str = sc.nextLine();
          StringTokenizer tok = new StringTokenizer(str, " ");
          while(tok.hasMoreTokens()) {
              String s = tok.nextToken();
              arr[j][count++] = s.charAt(0);
              if(s.charAt(0) == 'B') {
                  startI = j;
                  startJ = m-1;
              }
          }
      }
      Map<String, Boolean> tracker = new HashMap<String, Boolean>();
      catchP(arr, tracker, 0, n, m, startI, startJ);
      // find min over minSeen here.
      int min = Integer.MAX_VALUE;
      for(Integer minI : minSeen) {
          if( min > minI) {
              min = minI;
          }
      }
      System.out.println(min);
  }
 }
 
 static boolean seenAlready(Map<String, Boolean> tracker, int n, int m) {
     String key = Integer.toString(n) + "." + Integer.toString(m);
     return tracker.containsKey(key);
 }
 
 static boolean isValid(int row, int col, int n, int m) {
     if( row >= 0 && row <= n-1 && col >=0 && col <= m-1) {
         return true;
     }
     return false;
 }
 
 static void catchP(char[][] arr, Map<String, Boolean> tracker, int len, int n, int m, int startI, int startJ) {
     Map<String, Boolean> currentTracker = new HashMap<String, Boolean>();
     if(arr[startI][startJ] == 'C') {
         minSeen.add(len);
     } else if ( arr[startI][startJ] == 'D' || arr[startI][startJ]=='.' && seenAlready(tracker, startI, startJ) ) {
         return;
     } else if ( arr[startI][startJ]=='.' && !seenAlready(tracker, startI, startJ) || arr[startI][startJ] == 'B' ) {
         // copy currentTracker same as tracker.
         tracker.forEach(currentTracker::putIfAbsent);
         String newKey = Integer.toString(startI) + "." + Integer.toString(startJ);
         currentTracker.put(newKey, true);
         if( isValid(startI, startJ-1, n, m)) {
             catchP(arr, currentTracker, len+1, n, m, startI, startJ-1);
         }
         if( isValid(startI-1, startJ, n , m)) {
             catchP(arr, currentTracker, len+1, n, m, startI-1, startJ);
         }
         if( isValid(startI, startJ+1, n, m) ) {
             catchP(arr, currentTracker, len+1, n, m, startI, startJ+1);
         }
         if( isValid(startI+1, startJ, n, m) ) {
             catchP(arr, currentTracker, len+1, n, m, startI+1, startJ);
         }
     }
 }

Test execute it here.