ARST打卡第37周[37/521]

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/*

TreeNode *root = new TreeNode(1);
root->left = new ... 2
....
// Please implement a class called NodeIterator, so that:
NodeIterator i(root);
i.hasNext(); // true
i.next(); // 4
i.next(); // 2
i.next(); // 1
i.next(); // 5
i.next(); // 3
i.hasNext(); // false
i.next(); // throw
*/
TreeNode {
  int val;
  TreeNode *left;
  TreeNode *right;
}

class NodeIterator {
    public :
        NodeIterator(TreeNode * root){
            if(root == nullptr){
                return ;
            }

            TreeNode * tp = root;

            check();
        }

        // 建议使用着先访问hasNext函数
        bool hasNext(){
            return !s.empty();
        }

        int next(){
            if(!hasNext()) throw exception("No more data.");

            tp = s.top();
            int ans = tp -> val;

            s.pop();

            tp = tp -> right;

            check();

            return ans;
         }

        void check(){
            // 自己不为nullptr放入
            while(tp != nullptr){
                s.push(tp);
                tp = tp -> left;
            }
        }


    private:
        stack<TreeNode*> s;
        TreeNode * tp;
}

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## 显示最后1000行
    tail -n 1000

## 从1000行开始显示，显示1000行以后的
    tail -n +1000

## 显示前面1000行
    head -n 1000