leetcode@ [173] Binary Search Tree Iterator (InOrder traversal)
https://leetcode.com/problems/binary-search-tree-iterator/
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.
/** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class BSTIterator { public: queue<int> Q; public: BSTIterator(TreeNode *root) { inOrder(root, Q); } void inOrder(TreeNode* root, queue<int>& Q) { if(root != NULL) { inOrder(root->left, Q); Q.push(root->val); inOrder(root->right, Q); } } /** @return whether we have a next smallest number */ bool hasNext() { return !Q.empty(); } /** @return the next smallest number */ int next() { int next_min = Q.front(); Q.pop(); return next_min; } }; /** * Your BSTIterator will be called like this: * BSTIterator i = BSTIterator(root); * while (i.hasNext()) cout << i.next(); */