Python实现二叉树的前序遍历、中序遍历

计算根节点到叶子节点的所组成的数字（1247， 125， 1367）以及叶子节点到根节点组成的数字（7421， 521， 8631），其二叉树树型结构如下

计算从根节点到叶子节点组成的数字，本质上来说就是二叉树的先序便利的变形，只在每次递归遍历过程中，将上一步计算的结果传到下一轮的递归预算中，其代码如下：

 class Tree(object):

     def __init__(self, val):
         self.value = '%s' % str(val)
         self.value = val
         self.lchild = None
         self.rchild = None

     def __str__(self):
         returnList = []
         returnList.append(self)
         for i in len(returnList):
             node = returnList[i]
             returnList.append(node.lchild)
             returnList.append(node.rchild)

         return str(returnList)

     def _repr_(self):
         return '<N:%s>' % self.value

 def TreeSum(depth, value, tree):
     if not tree.lchild and not tree.rchild:
         print '%s value: %s' % (depth * '\t', value)
     else:
         #import pdb;pdb.set_trace()
         if tree.lchild:
             print '%sT%s->lchild --->>>' % (depth * '\t', tree.value)
             TreeSum(depth+1, value * 10 + tree.lchild.value, tree.lchild)
         if tree.rchild:
             print '%sT%s->rchild %s' % (depth * '\t', tree.value, '--->>>'.decode().encode('GBK'))
             TreeSum(depth+1, value * 10 + tree.rchild.value, tree.rchild)

 def RTreeSum(depth, value, tree):
    if tree.lchild or tree.rchild:
         #import pdb;pdb.set_trace()
         if tree.lchild:
             print '%sT%s->lchild --->>>' % (depth * '\t', tree.lchild.value)
             RTreeSum(depth+1, tree.lchild.value * pow(10, depth) + value, tree.lchild)
         if tree.rchild:
             print '%sT%s->rchild --->>>' % (depth * '\t', tree.rchild.value)
             RTreeSum(depth+1, tree.rchild.value * pow(10, depth) + value, tree.rchild)
    else:
         print '%s value: %s' % (depth * '\t', value)

 if __name__ == '__main__':
     root = Tree(1)
     t2 = Tree(2)
     t3 = Tree(3)
     t4 = Tree(4)
     t5 = Tree(5)
     t6 = Tree(6)
     t7 = Tree(7)
     t8 = Tree(8)
     root.lchild = t2
     root.rchild = t3
     t2.lchild = t4
     t2.rchild = t5
     t3.lchild = None
     t3.rchild = t6
     t4.lchild = t7
     t4.rchild = None
     t6.rchild = t8

     print 'Tree Sum:'
     TreeSum(0, 1, root)

     print 'Reverse Tree Sum:'
     RTreeSum(1, 1, root)

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其中TreeSum是计算跟节点到叶子节点的数字组合， RTreeSum 是计算叶子节点到根节点的组合

输出结果如下：

 Tree Sum:
 T1->lchild --->>>
     T2->lchild --->>>
         T4->lchild --->>>
              value: 1247
     T2->rchild --->>>
          value: 125
 T1->rchild --->>>
     T3->rchild --->>>
         T6->rchild --->>>
              value: 1368
 Reverse Tree Sum:
     T2->lchild --->>>
         T4->lchild --->>>
             T7->lchild --->>>
                  value: 7421
         T5->rchild --->>>
              value: 521
     T3->rchild --->>>
         T6->rchild --->>>
             T8->rchild --->>>
                  value: 8631