【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;}