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题目：
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.
代码：
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) { if ( !root ) return NULL; if ( p->val>q->val ) swap(p, q); if ( root->val>=p->val && root->val<=q->val ) { return root; } else if ( root->val < p->val ) { return Solution::lowestCommonAncestor(root->right, p, q); } else { return Solution::lowestCommonAncestor(root->left, p, q); } } };
tips：
由于BST是数据有序的，因此找公共祖先要容易一些。
参考：http://bookshadow.com/weblog/2015/07/11/leetcode-lowest-common-ancestor-binary-search-tree/
【Lowest Common Ancestor of a Binary Search Tree】cpp
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原文地址：http://www.cnblogs.com/xbf9xbf/p/4645131.html
