Contiguous Regions In Matrix

contiguousRegions.java

  public static String point(int x, int y) {
    return String.format("%sx%s", x, y);
  }
                         
  public static int contiguousRegions(int[][] matrix) {
    var seen = new HashSet<String>();
    var count = 0;
    
    for (int i = 0; i < matrix.length; ++i) {
      for (int k = 0; k < matrix[0].length; ++ k) {
        int v = matrix[i][k];
        count += dfsVisit(i, k, matrix, v, seen) > 0 ? 1 : 0;
      }
    }
    
    return count;
  }
  
  public static int dfsVisit(int i, int k, int[][] matrix, int v, HashSet<String> seen) {
    if (matrix[i][k] != v || !seen.add(point(i, k))) {
      return 0;
    }
    
    int c = 1;
    
    if (i + 1 < matrix.length) {
      c += dfsVisit(i + 1, k, matrix, v, seen);
    }
    
    if (i - 1 >= 0) {
      c += dfsVisit(i - 1, k, matrix, v, seen);
    }
    
    if (k + 1 < matrix[0].length) {
      c += dfsVisit(i, k + 1, matrix, v, seen);
    }
    
    if (k - 1 >= 0) {
      c += dfsVisit(i, k - 1, matrix, v, seen);
    }
    
    return c;
  }