leetcode 173. Binary Search Tree Iterator

Posted 2022-07-29 hwd9654

 

class BSTIterator 
    private Stack<TreeNode> stack;
    public BSTIterator(TreeNode root) 
        stack = new Stack<>();
        while(root != null)
            stack.push(root);
            root = root.left;
        
    
    
    /** @return the next smallest number */
    public int next() 
        TreeNode cur = stack.pop();
        TreeNode tmp = cur;
        if(tmp != null)
            tmp = tmp.right;
            while(tmp != null)
                stack.push(tmp);
                tmp = tmp.left;
            
        
        
        return cur.val;
    
    
    /** @return whether we have a next smallest number */
    public boolean hasNext() 
        
        return !stack.isEmpty();