main.cpp

/// Source : https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/
/// Author : liuyubobobo
/// Time   : 2017-11-18

#include <iostream>
#include <cassert>

using namespace std;


/// Definition for a binary tree node.
struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};


/// Recursive
/// Time Complexity: O(lgn), where n is the node's number of the tree
/// Space Complexity: O(h), where h is the height of the tree
class Solution {
public:
    TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {

        assert(p != NULL && q != NULL);

        if(root == NULL)
            return NULL;

        if(p->val < root->val && q->val < root->val)
            return lowestCommonAncestor(root->left, p, q);
        if(p->val > root->val && q->val > root->val)
            return lowestCommonAncestor(root->right, p, q);

        assert(p->val == root->val || q->val == root->val
                || (root->val - p->val) * (root->val - q->val) < 0);

        return root;
    }
};

int main() {

    return 0;
}