无涯教程-Python - 树遍历遍历是访问树的所有节点并且也可以打印其值的过程，因为所有节点都是通过边连接的，所以无

遍历是访问树的所有节点并且也可以打印其值的过程，因为所有节点都是通过边连接的，所以无涯教程总是从根节点开始，也就是说，不能随机访问树中的节点，无涯教程使用三种方式遍历树-

前序遍历
中序遍历
后序遍历

前序遍历

在这种遍历方法中，首先访问左子树，然后访问根，然后再访问右子树。应该永远记住，每个节点都可能代表一个子树本身。

在下面的python程序中，使用Node类为根节点以及左右节点创建占位符，然后，创建一个插入函数以将数据添加到树中，最后，通过创建一个空列表并先添加左节点，然后再添加根节点或父节点来实现有序遍历逻辑，最后，添加左节点以完成顺序遍历。

class Node:
</span><span class="kwd">def</span><span class="pln"> __init__</span><span class="pun">(</span><span class="kwd">self</span><span class="pun">,</span><span class="pln"> data</span><span class="pun">):</span><span class="pln">

    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">=</span><span class="kwd">None</span><span class="pln">
    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">=</span><span class="kwd">None</span><span class="pln">
    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">=</span><span class="pln">data

# 插入节点
def insert(self, data):
    </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
        </span><span class="kwd">if</span><span class="pln"> data </span><span class="pun">&lt;</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
            </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left </span><span class="kwd">is</span><span class="pln"> </span><span class="kwd">None</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">=</span><span class="typ">Node</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
            </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">.</span><span class="pln">insert</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
        </span><span class="kwd">elif</span><span class="pln"> data </span><span class="pun">&gt;</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
            </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right </span><span class="kwd">is</span><span class="pln"> </span><span class="kwd">None</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">=</span><span class="typ">Node</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
            </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">.</span><span class="pln">insert</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
    </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
        </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">=</span><span class="pln">data

#打印树
def PrintTree(self):
if self.left:
self.left.PrintTree()
print( self.data),
if self.right:
self.right.PrintTree()
# 中序遍历
# Left -> Root -> Right
def inorderTraversal(self, root):
res=[]
if root:
res=self.inorderTraversal(root.left)
res.append(root.data)
res=res + self.inorderTraversal(root.right)
return res
root=Node(27)
root.insert(14)
root.insert(35)
root.insert(10)
root.insert(19)
root.insert(31)
root.insert(42)
print(root.inorderTraversal(root))

执行以上代码后，将产生以下输出-

[10, 14, 19, 27, 31, 35, 42]

中序遍历

在这种遍历方法中，首先访问根节点，然后是左子树，最后是右子树。

在下面的python程序中，使用Node类为根节点以及左右节点创建占位符，然后，创建一个插入函数以将数据添加到树中，最后，通过创建一个空列表并先添加根节点，然后再添加左节点来实现预遍历逻辑，最后，添加右节点以完成预遍历。

class Node:
</span><span class="kwd">def</span><span class="pln"> __init__</span><span class="pun">(</span><span class="kwd">self</span><span class="pun">,</span><span class="pln"> data</span><span class="pun">):</span><span class="pln">

    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">=</span><span class="kwd">None</span><span class="pln">
    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">=</span><span class="kwd">None</span><span class="pln">
    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">=</span><span class="pln">data

# 插入节点
def insert(self, data):
    </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
        </span><span class="kwd">if</span><span class="pln"> data </span><span class="pun">&lt;</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
            </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left </span><span class="kwd">is</span><span class="pln"> </span><span class="kwd">None</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">=</span><span class="typ">Node</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
            </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">.</span><span class="pln">insert</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
        </span><span class="kwd">elif</span><span class="pln"> data </span><span class="pun">&gt;</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
            </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right </span><span class="kwd">is</span><span class="pln"> </span><span class="kwd">None</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">=</span><span class="typ">Node</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
            </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">.</span><span class="pln">insert</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
    </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
        </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">=</span><span class="pln">data

# 打印树
def PrintTree(self):
if self.left:
self.left.PrintTree()
print( self.data),
if self.right:
self.right.PrintTree()
#前序遍历
# Root -> Left ->Right
def PreorderTraversal(self, root):
res=[]
if root:
res.append(root.data)
res=res + self.PreorderTraversal(root.left)
res=res + self.PreorderTraversal(root.right)
return res
root=Node(27)
root.insert(14)
root.insert(35)
root.insert(10)
root.insert(19)
root.insert(31)
root.insert(42)
print(root.PreorderTraversal(root))

执行以上代码后，将产生以下输出-

[27, 14, 10, 19, 35, 31, 42]

后序遍历

在这种遍历方法中，根节点是最后访问的，首先，无涯教程先遍历左侧子树，然后遍历右侧子树，最后遍历根节点。

在下面的python程序中，使用Node类为根节点以及左右节点创建占位符，然后，创建一个插入函数以将数据添加到树中，最后，通过创建一个空列表并先添加左节点，再添加右节点，实现后遍历逻辑，最后，添加根节点或父节点以完成后顺序遍历。

class Node:
</span><span class="kwd">def</span><span class="pln"> __init__</span><span class="pun">(</span><span class="kwd">self</span><span class="pun">,</span><span class="pln"> data</span><span class="pun">):</span><span class="pln">

    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">=</span><span class="kwd">None</span><span class="pln">
    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">=</span><span class="kwd">None</span><span class="pln">
    </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">=</span><span class="pln">data

# 插入节点
def insert(self, data):
    </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
        </span><span class="kwd">if</span><span class="pln"> data </span><span class="pun">&lt;</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
            </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left </span><span class="kwd">is</span><span class="pln"> </span><span class="kwd">None</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">=</span><span class="typ">Node</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
            </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">left</span><span class="pun">.</span><span class="pln">insert</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
        </span><span class="kwd">elif</span><span class="pln"> data </span><span class="pun">&gt;</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">:</span><span class="pln">
            </span><span class="kwd">if</span><span class="pln"> </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right </span><span class="kwd">is</span><span class="pln"> </span><span class="kwd">None</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">=</span><span class="typ">Node</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
            </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
                </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">right</span><span class="pun">.</span><span class="pln">insert</span><span class="pun">(</span><span class="pln">data</span><span class="pun">)</span><span class="pln">
    </span><span class="kwd">else</span><span class="pun">:</span><span class="pln">
        </span><span class="kwd">self</span><span class="pun">.</span><span class="pln">data</span><span class="pun">=</span><span class="pln">data

# 打印树
def PrintTree(self):
if self.left:
self.left.PrintTree()
print( self.data),
if self.right:
self.right.PrintTree()
# 后序遍历
# Left ->Right -> Root
def PostorderTraversal(self, root):
res=[]
if root:
res=self.PostorderTraversal(root.left)
res=res + self.PostorderTraversal(root.right)
res.append(root.data)
return res
root=Node(27)
root.insert(14)
root.insert(35)
root.insert(10)
root.insert(19)
root.insert(31)
root.insert(42)
print(root.PostorderTraversal(root))

执行以上代码后，将产生以下输出-

[10, 19, 14, 31, 42, 35, 27]

无涯教程-Python - 树遍历

前序遍历

中序遍历

后序遍历

参考链接