LeetCode 【235. Lowest Common Ancestor of a Binary Search Tree】-优快云博客

本文介绍了一种寻找二叉搜索树中两给定节点的最低公共祖先的有效方法。利用二叉搜索树的特性，通过比较节点值来确定公共祖先的位置。提供了详细的算法思路及C++实现代码。

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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.

思路1.分别和当前节点比较（最开始是根节点）如果p->val和q->val一个大于当前节点值，一个小于当前节点值，则表示当前节点是他们的最低公共祖先，如果两个的大于当前节点的值，则递归调用右子树，如果都小于，则递归调用左子树。

/**
 * 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)
        {

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

转载于:https://www.cnblogs.com/rockwall/p/5744265.html