leecode第二百三十题（二叉搜索树中第K小的元素）

/**
 * 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 k_time;
    int temp;
    void kth_min(TreeNode* root)
    {
        if(root->left!=NULL)//不停找左节点
            kth_min(root->left);
        
        if(k_time>0)//查看k减少到0没
            k_time--;
        else 
            return;
        if(k_time==0)//如果为0，把当前节点赋给temp
            temp=root->val;
        
        if(root->right!=NULL)
            kth_min(root->right);
    }
    
    int kthSmallest(TreeNode* root, int k) {
        k_time=k;
        kth_min(root);
        return temp;
        
    }
};