173. Binary Search Tree Iterator
本题考的是使用stack去非递归的中序遍历二叉搜索树
/**
* 本题考的是使用stack去非递归的中序遍历二叉搜索树
*
*/
class BSTIterator {
//Definition for a binary tree node.
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
stack<TreeNode*>s;
TreeNode* current = NULL;
public:
BSTIterator(TreeNode *root) {
current = root;
}
/** @return whether we have a next smallest number */
bool hasNext() {
return current != NULL || !s.empty();
}
/** @return the next smallest number */
int next() {
while (current) {
s.push(current);
current = current->left;
}
current = s.top();
s.pop();
int val = current->val;
current = current->right;
return val;
}
};
