Leetcode235

Lowest Common Ancestor of a Binary Search Tree

Solution:

#include 

using namespace std;


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) {

        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);

        return root;

    }
};

总结：
说一下二分搜索树的概念吧：每个结点的键值大于左孩子，每个结点的键值小于右孩子，以左右孩子为根的子树仍为二分搜索树。这个概念本身就是递归定义的。