题解：二叉树的中序遍历

public class Solution {
    TreeNode res = null; 
    int count=0;
    TreeNode KthNode(TreeNode pRoot, int k) {
        if(pRoot==null||k==0) return null;
        helper(pRoot,k);
        return res;
    }
    
    void helper(TreeNode pRoot,int k){
        if(pRoot==null) return;
        
        helper(pRoot.left,k);
        count++;
        if(count==k){
            res = pRoot;
        }
        helper(pRoot.right,k);
        
    }
}