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