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/**
 * 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:
    int kthSmallest(TreeNode* root, int k) {
        if (root == NULL) return -1;
        int retVal = -1;
        int count = 0;
        findIt(root, k, count, retVal);
        return retVal;
    }
    
    void findIt(TreeNode* node, int k, int& count, int& ret) {
        if (count >= k) return;
        if (node->left != NULL) findIt(node->left, k, count, ret);
        count++;
        if (count == k) {
            ret = node->val;
            return;
        }
        if (node->right != NULL) findIt(node->right, k, count, ret);
    }
};