Lowest Common Ancestor of a Binary Search Tree

phlovexz

于 2016-06-07 16:03:18 发布

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分类专栏： LeetCode 文章标签： c语言

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本文介绍了一种寻找二叉搜索树中两个节点的最近公共祖先的方法。通过递归遍历，当根节点的值位于两个节点值之间时，该根节点即为最近公共祖先。若根节点值大于两个节点值，则在左子树中继续查找；反之，在右子树中查找。

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c++

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

python

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def lowestCommonAncestor(self, root, p, q):
        """
        :type root: TreeNode
        :type p: TreeNode
        :type q: TreeNode
        :rtype: TreeNode
        """
        if p.val > q.val:
            p,q = q,p

        if root.val>=p.val and root.val<=q.val:
            return root
        if root.val>p.val and root.val>q.val:
            return self.lowestCommonAncestor(root.left, p, q)
        else:
            return self.lowestCommonAncestor(root.right, p, q)