From : https://leetcode.com/problems/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 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.
Solution :
/**
* 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) return NULL;
small = p->val;
large = q->val;
if(small > large) {
int t = small^large;
small = t^small;
large = t^large;
}
return find(root);
}
TreeNode* find(TreeNode* root) {
int v = root->val;
if(v > large) return find(root->left);
else if(v < small) return find(root->right);
else return root;
}
private:
int small, large;
};