LeetCode Q235: 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.

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

view raw Q235.cpp hosted with ❤ by GitHub

	class Solution {
	public:
	TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
	TreeNode* res=NULL;
	if(root==NULL)
	return res;
	if(p->val>q->val)
	return lowestCommonAncestor(root, q, p);
	if(p->val<=root->val&&q->val>=root->val)
	res=root;
	if(p->val<root->val&&q->val<root->val)
	res=lowestCommonAncestor(root->left, p, q);
	if(p->val>root->val&&q->val>root->val)
	res=lowestCommonAncestor(root->right, p, q);
	return res;
	}
	};

view raw Q235Rnd3.cpp hosted with ❤ by GitHub