题目

binary-search-tree-iterator

2. 算法

* 直接模拟

3. 代码

class BSTIterator {
public:
    BSTIterator(TreeNode *root) {
        while (root) {
            s.push(root);
            root = root->left;
        }
    }

    /** @return whether we have a next smallest number */
    bool hasNext() {
        return !s.empty();
    }

    /** @return the next smallest number */
    int next() {
        TreeNode *n = s.top();
        s.pop();
        int res = n->val;
        if (n->right) {
            n = n->right;
            while (n) {
                s.push(n);
                n = n->left;
            }
        }
        return res;
    }
private:
    stack<TreeNode*> s;
};