Lowest Common Ancestor of a Binary Search Tree

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于 2015-07-19 20:57:03 发布

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分类专栏： C++算法题文章标签： Lowest Common Ancest C++ 算法

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本文探讨了在二叉搜索树中查找两个给定节点的最低公共祖先的方法，详细介绍了算法实现及执行结果。

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一、题目内容

Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.

According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

        _______6______
       /              \
    ___2__          ___8__
   /      \        /      \
   0      _4       7       9
         /  \
         3   5

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

二、代码实现

 TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
         if(root==NULL)
		 return NULL;
	 TreeNode* tmp=root;
	 while(1)
	 {
		 if((tmp->val<=p->val && tmp->val>=q->val)||(tmp->val>=p->val && tmp->val<=q->val))
			 return tmp;
		 else if(tmp->val<p->val && tmp->val<q->val)
			 tmp=tmp->right;
		 else if(tmp->val>p->val && tmp->val>q->val)
			 tmp=tmp->left;
	 }

三、执行结果