235. Lowest Common Ancestor of a Binary Search Tree

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 p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”

Given binary search tree: root = [6,2,8,0,4,7,9,null,null,3,5]

Example 1:

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
Output: 6
Explanation: The LCA of nodes 2 and 8 is 6.

Example 2:

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
Output: 2
Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

Note:

All of the nodes' values will be unique.
p and q are different and both values will exist in the BST.

题意：寻找二叉搜索树上，两个结点的公共祖先。

方法一：递归，当p,q都在左子树上时，递归搜索左子树。当p,q 都在右子树上时，递归搜索右子树。否则返回root。

/**
 * 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;
    }   
};

来源：CSDN

作者：万里归来少年心

链接：https://blog.csdn.net/liyazhen2011/article/details/104132656

标签

common