C#实现二叉树的前序、中序、后序遍历。
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public
class
BinaryTreeNode
{
int
value;
BinaryTreeNode left;
BinaryTreeNode right;
/// <summary>
/// 前序遍历
/// </summary>
/// <param name="tree"></param>
public
static
void
PreOrder(BinaryTreeNode tree)
{
if
(tree ==
null
)
return
;
System.Console.Write(tree.value +
" "
);
PreOrder(tree.left);
PreOrder(tree.right);
}
/// <summary>
/// 前序遍历循环实现
/// </summary>
/// <param name="tree"></param>
public
static
void
PreOrderLoop(BinaryTreeNode tree)
{
if
(tree ==
null
)
return
;
Stack<BinaryTreeNode> stack =
new
Stack<BinaryTreeNode>();
BinaryTreeNode node = tree;
while
(node !=
null
|| stack.Any()){
if
(node !=
null
)
{
stack.Push(node);
System.Console.Write(node.value +
" "
);
node = node.left;
}
else
{
var
item = stack.Pop();
node = item.right;
}
}
}
/// <summary>
/// 中序遍历
/// </summary>
/// <param name="tree"></param>
public
static
void
InOrder(BinaryTreeNode tree)
{
if
(tree ==
null
)
return
;
InOrder(tree.left);
System.Console.Write(tree.value +
" "
);
InOrder(tree.right);
}
/// <summary>
/// 中序遍历循环实现
/// </summary>
/// <param name="tree"></param>
public
static
void
InOrderLoop(BinaryTreeNode tree)
{
if
(tree ==
null
)
return
;
Stack<BinaryTreeNode> stack =
new
Stack<BinaryTreeNode>();
BinaryTreeNode node = tree;
while
(node !=
null
|| stack.Any())
{
if
(node !=
null
)
{
stack.Push(node);
node = node.left;
}
else
{
var
item = stack.Pop();
System.Console.Write(item.value +
" "
);
node = item.right;
}
}
}
/// <summary>
/// 后序遍历
/// </summary>
/// <param name="tree"></param>
public
static
void
PostOrder(BinaryTreeNode tree)
{
if
(tree ==
null
)
return
;
PostOrder(tree.left);
PostOrder(tree.right);
System.Console.Write(tree.value +
" "
);
}
/// <summary>
/// 后序遍历循环实现1
/// </summary>
/// <param name="tree"></param>
public
static
void
PostOrderLoop(BinaryTreeNode tree)
{
if
(tree ==
null
)
return
;
Stack<BinaryTreeNode> stack =
new
Stack<BinaryTreeNode>();
BinaryTreeNode node = tree;
BinaryTreeNode pre =
null
;
stack.Push(node);
while
(stack.Any())
{
node = stack.Peek();
if
((node.left ==
null
&& node.right ==
null
) ||
(pre !=
null
&& (pre == node.left || pre == node.right)))
{
System.Console.Write(node.value +
" "
);
pre = node;
stack.Pop();
}
else
{
if
(node.right !=
null
)
stack.Push(node.right);
if
(node.left !=
null
)
stack.Push(node.left);
}
}
}
/// <summary>
/// 后续遍历循环实现2
/// </summary>
/// <param name="tree"></param>
public
static
void
PostOrderLoop2(BinaryTreeNode tree)
{
HashSet<BinaryTreeNode> visited =
new
HashSet<BinaryTreeNode>();
Stack<BinaryTreeNode> stack =
new
Stack<BinaryTreeNode>();
BinaryTreeNode node = tree;
while
(node !=
null
|| stack.Any())
{
if
(node !=
null
)
{
stack.Push(node);
node = node.left;
}
else
{
var
item = stack.Peek();
if
(item.right !=
null
&& !visited.Contains(item.right))
{
node = item.right;
}
else
{
System.Console.Write(item.value +
" "
);
visited.Add(item);
stack.Pop();
}
}
}
}
}
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本文转自 许大树 51CTO博客，原文链接：http://blog.51cto.com/abelxu/1966963，如需转载请自行联系原作者
