Binary Search Tree Iterator--LeetCode

標籤：c++   leetcode   演算法   

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, whereh is the height of the tree.

思路：依靠棧資料結構，然後中序遍曆的思想

class BSTIterator {public:    BSTIterator(BinTree *root) {      while(!st.empty())        sk.pop();      BinTree* temp=root;      while(temp != NULL)      {        sk.push(temp);        temp = temp->left;      }      }    /** @return whether we have a next smallest number */    bool hasNext() {        return sk.empty();    }    /** @return the next smallest number */    int next() {        BinTree* res = sk.top();        sk.pop();        BinTree* temp = res->right;        while(temp != NULL)        {          sk.push(temp);          temp = temp->left;        }        return res->value;    }private:        stack<BinTree*> sk;};

Binary Search Tree Iterator--LeetCode