Leetcode problem solving - 230 The k-th smallest element in the binary search tree

public int kthSmallest(TreeNode root, int k) {
    
        int i = 1;
        Stack<TreeNode> stack = new Stack<>();
        TreeNode node = root;
        while (!stack.isEmpty()||node!=null){
    
            while (node!=null){
    
                stack.push(node);
                node = node.left;
            }
            node = stack.pop();
            if (i==k) return node.val;
            i++;
            node = node.right;
        }
        return -1;
    }

Ideas ： It is improved on the basis of the medium order iteration scheme ：

• Judge at the access element , And count
• When i==k, That is, the current number of trees K Element time , Returns the value of the current node