leetcode: (235) Lowest Common Ancestor of a Binary Search Tree

最新推荐文章于 2022-11-16 17:34:17 发布

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最新推荐文章于 2022-11-16 17:34:17 发布

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分类专栏： leetcode algorithms 文章标签： algorithms leetcode 二叉树

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本文介绍了一种在二叉搜索树(BST)中寻找两节点间最低公共祖先(LCA)的有效方法。通过遍历BST，当两节点位于当前节点的不同侧时，则当前节点即为所求LCA。此算法适用于计算机科学与数据结构的学习。

【Question】

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.

方法：最小的祖先，就是一个两个结点不在同一个分支上的时候，就是出现一左一右的时候

/**
 * 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) {
       while(root!=NULL)
       {
           if(root->val>p->val&&root->val>q->val)
           {
               root=root->left;
           }
           else if(root->val<p->val&&root->val<q->val)
           {
               root=root->right;
           }
           else return root;
       }
       return root; 
    }
};