Binary Search Tree Iterator

Description

Design an iterator over a binary search tree with the following rules:

• Elements are visited in ascending order (i.e. an in-order traversal)
• next() and hasNext() queries run in O(1) time in average.

Example
For the following binary search tree, in-order traversal by using iterator is [1, 6, 10, 11, 12]
   10
 /    \
1      11
 \       \
  6       12

Challenge Extra memory usage O(h), h is the height of the tree.

• We are here, indorder traversal

Super Star: Extra memory usage O(1)

• Use binary search O(logn) S(1)

Link

Lintcode_ladder

Method

1. x
2. x

Example

1. 1

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 * Example of iterate a tree:
 * BSTIterator iterator = BSTIterator(root);
 * while (iterator.hasNext()) {
 *    TreeNode * node = iterator.next();
 *    do something for node
 */
class BSTIterator {
public:
    // @param root: The root of binary tree.
    BSTIterator(TreeNode *root) {
        // write your code here
        TreeNode* tmp = root;
        while (tmp) {
            stk.push(tmp);
            tmp = tmp->left;
        }
    }
    // @return: True if there has next node, or false
    bool hasNext() {
        // write your code here
        return !stk.empty();
    }
    // @return: return next node
    TreeNode* next() {
        // write your code here
        next_min = stk.top();
        stk.pop();
        TreeNode* tmp = next_min->right;
        while (tmp) {
            stk.push(tmp);
            tmp = tmp->left;
        }
        return next_min;
    }
private:
    // TreeNode* src;
    TreeNode* next_min;
    stack<TreeNode*> stk;
};

Similar problems

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