How to print a tree-ADT

写和树相关的代码的时候老是不方便debug，因为树形结构虽然能够代码构造出来

但是如果能够有个很好的方法可视化就更好了。

前些天看到一个MIT的代码片段，感激～....

一开始你可能会想到一种比较简单的迭代实现，就像之前我做的

1. void putout(int S, int *n)  

http://blog.csdn.net/cinmyheart/article/details/43086233

这个函数会打印一个三角形

而我看到MIT老师准备的教学用的Python代码时就眼前一亮的感觉，有了一种更“精准的“打印三角形的策略——基于递归。

    def _str(self):
        """Internal method for ASCII art."""
        label = str(self.key)
        if self.left is None:
            left_lines, left_pos, left_width = [], 0, 0
        else:
            left_lines, left_pos, left_width = self.left._str()
        if self.right is None:
            right_lines, right_pos, right_width = [], 0, 0
        else:
            right_lines, right_pos, right_width = self.right._str()
        middle = max(right_pos + left_width - left_pos + 1, len(label), 2)
        pos = left_pos + middle // 2
        width = left_pos + middle + right_width - right_pos
        while len(left_lines) < len(right_lines):
            left_lines.append(' ' * left_width)
        while len(right_lines) < len(left_lines):
            right_lines.append(' ' * right_width)
        if (middle - len(label)) % 2 == 1 and self.parent is not None and            self is self.parent.left and len(label) < middle:
            label += '.'
        label = label.center(middle, '.')
        if label[0] == '.': label = ' ' + label[1:]
        if label[-1] == '.': label = label[:-1] + ' '
        lines = [' ' * left_pos + label + ' ' * (right_width - right_pos),
                 ' ' * left_pos + '/' + ' ' * (middle-2) +
                 '\\' + ' ' * (right_width - right_pos)] +           [left_line + ' ' * (width - left_width - right_width) + right_line
           for left_line, right_line in zip(left_lines, right_lines)]
        return lines, pos, width
    def __str__(self):
        return '\n'.join(self._str()[0])

（过段时间我再注释，先把代码贴出来）

下面是个的改动版本，还有点需要完善的地方，不过还能凑合用：

      def __str__(self):

          def recurse(node) :
               if node is None:
                   return [], 0, 0
               else :
                   left_lines, left_pos, left_width = recurse(node.left)
                   right_lines, right_pos, right_width = recurse(node.right)

		   label = str(node.number)

		   middle = max(right_pos + left_width - left_pos +1, len(label), 2)
		   pos    = left_pos + middle//2
		   width  = left_pos + middle + right_width - right_pos

                   while len(left_lines) < len(right_lines) :
                       left_lines.append(' ' * left_width)
                   while len(right_lines) < len(left_lines) :
                       right_lines.append(' ' * right_width)

		   line   = [' ' * left_pos + label + ' ' * (right_width-right_pos + 1),
			     ' ' * left_pos + '/' + 
                             ' ' * (middle-2) + '\\' +
			     ' ' * (right_width - right_pos)
                            ] +                             [
				    left_line + 
				    ' ' * (width - left_width - right_width) +
				    right_line 
				    for left_line, right_line 
				    in zip(left_lines, right_lines)
                            ]

		   if node is self.root :
		       return line
		   else :
		       return line, pos, width

          if self.root is None :
               return '<Empty tree>'

          output = recurse(self.root)
          for i in range(1, len(output)-2) :
              output[0] += '\n' + output[i]

          return output[0]

demo:

大体的树形结构和层次是清楚的

后续会update,把原理讲清楚。。。递归实现

How to print a tree-ADT ? 打印树形结构的算法