C++简洁代码（中序遍历）：

C++简洁代码：

class Solution {
public:
    TreeNode* KthNode(TreeNode* pRoot, int k) {
        stack<TreeNode*> stk;
        TreeNode* cur = pRoot;
        while(cur || stk.size()) {
            while(cur) {
                stk.push(cur);
                cur = cur->left;
            }
            cur = stk.top();
            stk.pop();
            if(-- k == 0) return cur;
            cur = cur->right;
        }
        return nullptr;
    }
};