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解题思路:
- 二叉搜索树的中序遍历是递增的;
- 遍历后的第k个元素即为第k小;
/**
* 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:
void inorderTraversal(TreeNode* root, vector<int>& v)
{
if(root == NULL)
return;
inorderTraversal(root->left, v);
v.push_back(root->val);
inorderTraversal(root->right, v);
}
int kthSmallest(TreeNode* root, int k)
{
vector<int> ret;
inorderTraversal(root, ret);
return ret[k - 1];
}
};