Leetcode:Binary Search Tree Iterator

标签：bst

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.

    即找出二叉查找树中最小的元素。

    思路：找最小值，可以参考中序遍历，借助栈！每弹出一个元素，才增加栈中元素，不用马上遍历整颗树!

实现代码：

class BSTIterator {
    stack<TreeNode *> myStack;
public:
    BSTIterator(TreeNode *root) {
        TreeNode *node=root;
        while(node!=NULL)
        {
            myStack.push(node);
            node = node->left;
        }
    }

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

    /** @return the next smallest number */
    int next() {
        TreeNode *tmpNode = myStack.top();
        int res = tmpNode->val; 
        myStack.pop();
        
        tmpNode=tmpNode->right;
        while(tmpNode!=NULL)
        {
            myStack.push(tmpNode);
            tmpNode = tmpNode->left;
        }
        return res;
    }
};

Leetcode:Binary Search Tree Iterator

标签：bst

原文地址：http://blog.csdn.net/wolongdede/article/details/44918711