235. Lowest Common Ancestor of a Binary Search Tree --LeetCode Record

原创于 2016-07-17 01:31:01 发布 · 225 阅读

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本文介绍了一种在二叉搜索树中寻找两个指定节点的最低公共祖先的方法。通过递归地比较节点值，算法能高效定位目标节点。文章包含了一个C++实现示例。

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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

/**
 * 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) {
        // 同在右子树
        if ( root->val < p->val && root->val < q->val ) {
            return lowestCommonAncestor(root->right, p, q);
        }

        // 同在左子树
        if ( root->val > p->val && root->val > q->val ) {
            return lowestCommonAncestor(root->left, p, q);
        }

        // 有相等情况
        return root;
    }
};