【数据结构】求二叉树中两个结点最近的公共祖先

对于两个结点最近的公共祖先，有三种情况：

1，该二叉树是一棵二叉搜索树

struct TreeNode
{
int _value;
TreeNode* _left;
TreeNode* _right;

TreeNode(int x)
: _value(x)
, _left(NULL)
, _right(NULL)
{}
};
TreeNode* LowestAncestor(TreeNode* _root, TreeNode* node1, TreeNode* node2)
{
int m1 = min(node1->_value, node2->_value);
int m2 = max(node1->_value, node2->_value);
while (true)
{
if (_root->_value > m2)
{
_root = _root->_left;
}
else if (_root->_value < m1)
{
_root = _root->_right;
}
else
{
break;
}
}
return _root;
}2，该二叉树是一棵具有三叉链的二叉树
struct TreeNode
{
int _value;
TreeNode* _left;
TreeNode* _right;
TreeNode* _parent;

TreeNode(int x)
:_value(x)
, _left(NULL)
, _right(NULL)
, _parent(NULL)
{}
};

TreeNode* LowestAncestor(TreeNode* _root, TreeNode* node1, TreeNode* node2)
{
TreeNode* cur = NULL;
while (node1 != NULL)
{
node1 = node1->_parent;
cur = node2;
while (cur != NULL)
{
if (node1 == cur->_parent)
{
return node1;
}
cur = cur->_parent;
}
}
}3，一般的普通二叉树：
struct TreeNode
{
int _value;
TreeNode* _left;
TreeNode* _right;

TreeNode(int x)
:_value(x)
, _left(NULL)
, _right(NULL)
{}
};

TreeNode* LowestAncestor(TreeNode* _root, TreeNode* node1, TreeNode* node2)
{
if (_root == NULL || _root == node1 || _root == node2)
{
return _root;
}
TreeNode* left = LowestAncestor(_root->_left, node1, node2);
TreeNode* right = LowestAncestor(_root->_right, node1, node2);

if (left != NULL&&right = !NULL)
{
return _root;
}
return left = NULL ? right : left;
}