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21
Dec

Printing Binary Trees in Ascii

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Here we are not going to discuss what binary trees are (please refer this, if you are looking for binary search trees), or their operations but printing them in ascii.

The below routine prints tree in ascii for a given Tree representation which contains list of nodes, and node structure is this

struct Tree 
{
  Tree * left, * right;
  int element;
};

This pic illustrates what the below routine does on canvas..
ascii tree

Here is the printing routine..

//prints ascii tree for given Tree structure
void print_ascii_tree(Tree * t) 
{
  asciinode *proot;
  int xmin, i;
  if (t == NULL) return;
  proot = build_ascii_tree(t);
  compute_edge_lengths(proot);
  for (i=0; i<proot->height && i < MAX_HEIGHT; i++) 
  {
    lprofile[i] = INFINITY;
  }
  compute_lprofile(proot, 0, 0);
  xmin = 0;
  for (i = 0; i < proot->height && i < MAX_HEIGHT; i++) 
  {
    xmin = MIN(xmin, lprofile[i]);
  }
  for (i = 0; i < proot->height; i++) 
  {
    print_next = 0;
    print_level(proot, -xmin, i);
    printf("\n");
  }
  if (proot->height >= MAX_HEIGHT) 
  {
    printf("(This tree is taller than %d, and may be drawn incorrectly.)\n",
           MAX_HEIGHT);
  }
  free_ascii_tree(proot); 
}

Auxiliary routines..

//This function prints the given level of the given tree, assuming
//that the node has the given x cordinate.
void print_level(asciinode *node, int x, int level) 
{
  int i, isleft;
  if (node == NULL) return;
  isleft = (node->parent_dir == -1);
  if (level == 0) 
  {
    for (i=0; i<(x-print_next-((node->lablen-isleft)/2)); i++) 
    {
      printf(" ");
    }
    print_next += i;
    printf("%s", node->label);
    print_next += node->lablen;
  } 
  else if (node->edge_length >= level) 
  {
    if (node->left != NULL) 
    {
      for (i=0; i<(x-print_next-(level)); i++) 
      {
        printf(" ");
      }
      print_next += i;
      printf("/");
      print_next++;
    }
    if (node->right != NULL) 
    {
      for (i=0; i<(x-print_next+(level)); i++) 
      {
        printf(" ");
      }
      print_next += i;
      printf("\\");
      print_next++;
    }
  } 
  else 
  {
    print_level(node->left, 
                x-node->edge_length-1, 
                level-node->edge_length-1);
    print_level(node->right, 
                x+node->edge_length+1, 
                level-node->edge_length-1);
  }
}
 
 
//This function fills in the edge_length and 
//height fields of the specified tree
void compute_edge_lengths(asciinode *node) 
{
  int h, hmin, i, delta;
  if (node == NULL) return;
  compute_edge_lengths(node->left);
  compute_edge_lengths(node->right);
 
  /* first fill in the edge_length of node */
  if (node->right == NULL && node->left == NULL) 
  {
    node->edge_length = 0;
  } 
  else 
  {
    if (node->left != NULL) 
    {
      for (i=0; i<node->left->height && i < MAX_HEIGHT; i++) 
      {
        rprofile[i] = -INFINITY;
      }
      compute_rprofile(node->left, 0, 0);
      hmin = node->left->height;
    } 
    else 
    {
      hmin = 0;
    }
    if (node->right != NULL) 
    {
      for (i=0; i<node->right->height && i < MAX_HEIGHT; i++) 
      {
        lprofile[i] = INFINITY;
      }
      compute_lprofile(node->right, 0, 0);
      hmin = MIN(node->right->height, hmin);
    } 
    else 
    {
      hmin = 0;
    }
    delta = 4;
    for (i=0; i<hmin; i++) 
    {
      delta = MAX(delta, gap + 1 + rprofile[i] - lprofile[i]);
    }
 
    //If the node has two children of height 1, then we allow the
    //two leaves to be within 1, instead of 2 
    if (((node->left != NULL && node->left->height == 1) ||
	      (node->right != NULL && node->right->height == 1))&&delta>4) 
    {
      delta--;
    }
 
    node->edge_length = ((delta+1)/2) - 1;
  }
 
  //now fill in the height of node
  h = 1;
  if (node->left != NULL) 
  {
    h = MAX(node->left->height + node->edge_length + 1, h);
  }
  if (node->right != NULL) 
  {
    h = MAX(node->right->height + node->edge_length + 1, h);
  }
  node->height = h;
}

asciinode * build_ascii_tree_recursive(Tree * t) 
{
  asciinode * node;
 
  if (t == NULL) return NULL;
 
  node = malloc(sizeof(asciinode));
  node->left = build_ascii_tree_recursive(t->left);
  node->right = build_ascii_tree_recursive(t->right);
 
  if (node->left != NULL) 
  {
    node->left->parent_dir = -1;
  }
 
  if (node->right != NULL) 
  {
    node->right->parent_dir = 1;
  }
 
  sprintf(node->label, "%d", t->element);
  node->lablen = strlen(node->label);
 
  return node;
}
 
 
//Copy the tree into the ascii node structre
asciinode * build_ascii_tree(Tree * t) 
{
  asciinode *node;
  if (t == NULL) return NULL;
  node = build_ascii_tree_recursive(t);
  node->parent_dir = 0;
  return node;
}
 
//Free all the nodes of the given tree
void free_ascii_tree(asciinode *node) 
{
  if (node == NULL) return;
  free_ascii_tree(node->left);
  free_ascii_tree(node->right);
  free(node);
}
 
//The following function fills in the lprofile array for the given tree.
//It assumes that the center of the label of the root of this tree
//is located at a position (x,y).  It assumes that the edge_length
//fields have been computed for this tree.
void compute_lprofile(asciinode *node, int x, int y) 
{
  int i, isleft;
  if (node == NULL) return;
  isleft = (node->parent_dir == -1);
  lprofile[y] = MIN(lprofile[y], x-((node->lablen-isleft)/2));
  if (node->left != NULL) 
  {
    for (i=1; i <= node->edge_length && y+i < MAX_HEIGHT; i++) 
    {
      lprofile[y+i] = MIN(lprofile[y+i], x-i);
    }
  }
  compute_lprofile(node->left, x-node->edge_length-1, y+node->edge_length+1);
  compute_lprofile(node->right, x+node->edge_length+1, y+node->edge_length+1);
}
 
void compute_rprofile(asciinode *node, int x, int y) 
{
  int i, notleft;
  if (node == NULL) return;
  notleft = (node->parent_dir != -1);
  rprofile[y] = MAX(rprofile[y], x+((node->lablen-notleft)/2));
  if (node->right != NULL) 
  {
    for (i=1; i <= node->edge_length && y+i < MAX_HEIGHT; i++) 
    {
      rprofile[y+i] = MAX(rprofile[y+i], x+i);
    }
  }
  compute_rprofile(node->left, x-node->edge_length-1, y+node->edge_length+1);
  compute_rprofile(node->right, x+node->edge_length+1, y+node->edge_length+1);
}

Here is the asciii tree structure…

struct asciinode_struct
{
  asciinode * left, * right;
 
  //length of the edge from this node to its children
  int edge_length; 
 
  int height;      
 
  int lablen;
 
  //-1=I am left, 0=I am root, 1=right   
  int parent_dir;   
 
  //max supported unit32 in dec, 10 digits max
  char label[11];  
};

Download the ascii tree source code [note: I’d used msvc6 (which is a bit old one), so when you use new compilers you may get few compilations errors, fix them yourself or drop a msg over here..]

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