LeetCode - Binary Search Tree Iterator

最新推荐文章于 2022-06-10 17:57:38 发布

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最新推荐文章于 2022-06-10 17:57:38 发布

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分类专栏： Leetcode 文章标签： leetcode 二叉树 iterator

本文链接：https://blog.youkuaiyun.com/fenx91/article/details/46876817

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本文介绍如何实现一个在二叉搜索树中迭代的算法，重点在于利用栈来保存节点，确保每次调用next()和hasNext()方法时都能在平均O(1)时间内返回最小元素，并使用O(h)的内存，其中h为树的高度。

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Binary Search Tree Iterator

Total Accepted: 20470 Total Submissions: 69577 My Submissions

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.

Calling next() will return the next smallest number in the BST.

Note: next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.

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

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

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