一个漂亮的打印二叉树的程序

转自

// copyright @ L.J.SHOU Jan.16, 2014  
// a fancy binary tree printer  
#ifndef BINARY_TREE_PRINTER_H_  
#define BINARY_TREE_PRINTER_H_  

#include   
#include   
#include   
using std::vector;  
using std::cout;  
using std::endl;  
using std::max;  

void PrintBinaryTree(TreeNode *root);  

struct TreeNode  
{  
  TreeNode *left;  
  TreeNode *right;  
  int val;  
  TreeNode(int x=0)  
   : val(x), left(NULL), right(NULL){}  
};  

static int MaxLevel(TreeNode *root)  
{  
  if(root == NULL) return 0;  
  return max(MaxLevel(root->left), MaxLevel(root->right)) + 1;  
}  

// test whether all elements in vector are NULL  
static bool IsAllElementsNULL(const vector &nodes)  
{  
  vector::const_iterator it = nodes.begin();  

  while(it != nodes.end()){  
    if(*it) return false;   
    ++it;  
  }  
  return true;  
}  

static void PrintWhiteSpaces(int num)  
{  
  for(int i=0; icout << " ";  
}  

void PrintNode(vector &nodes, int level, int max_level)  
{  
  if(nodes.empty() || IsAllElementsNULL(nodes)) return; // exit  

  int floor = max_level - level;  
  int endge_lines = 1 << (max(floor-1, 0));  
  int first_spaces = (1 << floor) - 1;  
  int between_spaces = (1 << (floor+1)) - 1;  

  PrintWhiteSpaces(first_spaces);  

  // print the 'level' level   
  vector new_nodes;  
  vector::const_iterator it = nodes.begin();  
  for(; it != nodes.end(); ++it){  
    if(*it != NULL){  
      cout << (*it)->val;  
      new_nodes.push_back((*it)->left);  
      new_nodes.push_back((*it)->right);  
    }  
    else{  
      new_nodes.push_back(NULL);  
      new_nodes.push_back(NULL);  
      cout << " ";  
    }  
    PrintWhiteSpaces(between_spaces);  
  }  
  cout << endl;  

  // print the following /s and \s  
  for(int i=1; i<= endge_lines; ++i){  
    for(int j=0; jif(nodes[j] == NULL){  
        PrintWhiteSpaces(endge_lines + endge_lines + i + 1);  
        continue;  
      }  
      if(nodes[j]->left != NULL)  
        cout << "/";  
      else  
        PrintWhiteSpaces(1);  

      PrintWhiteSpaces(i+i-1);  

      if(nodes[j]->right != NULL)  
        cout << "\\";  
      else  
        PrintWhiteSpaces(1);  

      PrintWhiteSpaces(endge_lines + endge_lines - i);  
    }  
    cout << endl;  
  }  

  PrintNode(new_nodes, level+1, max_level);  

}  

// wrapper function  
void PrintBinaryTree(TreeNode *root)  
{  
  int max_level = MaxLevel(root);  
  vector nodes;  

  nodes.push_back(root);  

  PrintNode(nodes, 1, max_level);  
}  

#endif  

#if 0  
int main(void)  
{  
  TreeNode *root(NULL);  

  root = new TreeNode(1);  
  root->left = new TreeNode(2);  
  root->right = new TreeNode(3);  

  root->left->left = new TreeNode(4);  
  root->right->right = new TreeNode(7);  

  root->left->left->left = new TreeNode(8);  
  root->left->left->right = new TreeNode(9);  
  PrintBinaryTree(root);  

  root = Destroy(root);  
  return 0;  
}  
#endif