235. Lowest Common Ancestor of a Binary Search Tree.cpp

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