235. Lowest Common Ancestor of a Binary Search Tree（LCA）

最新推荐文章于 2022-02-12 22:47:33 发布

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最新推荐文章于 2022-02-12 22:47:33 发布

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本文链接：https://blog.youkuaiyun.com/qq_34594236/article/details/79633604

本文介绍了一种寻找二叉搜索树中两节点最低公共祖先(LCA)的有效算法。利用二叉搜索树的特性，该算法能快速定位LCA。例如，在节点2和8之间，LCA为6；而在节点2和4之间，LCA即为2。

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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.

 

题目思路：

由于给定的二叉搜索树，于是，如果给定的a个b都比根结点下，那么LCA一定在左子树中，反之亦然。

 
/**
 * 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 (p->val < root->val && q->val < root->val) return lowestCommonAncestor(root->left, p, q);
        if (p->val > root->val && q->val > root->val) return lowestCommonAncestor(root->right, p, q);
        return root;
    }
};
 

查看原文：http://iluhao.top/archives/631