LeetCode 230. Kth Smallest Element in a BST 动态演示

class Solution {
public:
    void helper(TreeNode* node, int& idx, int k, int& res){
        if(res!=INT_MAX)
            return;
        
        if(!node)
            return;
        
        //a(node)
        //lk("root",node)
        //dsp
        
        helper(node->left, idx, k, res);
        
        if(idx==k){
            res=node->val;
            //dsp
        }
        ++idx;
        helper(node->right, idx, k, res);
    }
    
    int kthSmallest(TreeNode* root, int k) {
        int idx=1;
        int res=INT_MAX;        
        //ahd(root)
        //a(res)
        //a(k)
        //a(idx)
        helper(root, idx, k, res);                
        return res;
    }
};