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/*In order traverse for BST gives the natural order of numbers. No need to use array.*/

/*Recursive:*/

int count = 0;
int result = Integer.MIN_VALUE;

public int kthSmallest(TreeNode root, int k) {
    traverse(root, k);
    return result;
}

public void traverse(TreeNode root, int k) {
    if(root == null) return;
    traverse(root.left, k);
    count ++;
    if(count == k) result = root.val;
    traverse(root.right, k);       
}

/*Iterative:*/

 public int kthSmallest(TreeNode root, int k) {
     Stack<TreeNode> stack = new Stack<TreeNode>();
     TreeNode p = root;
     int count = 0;
     
     while(!stack.isEmpty() || p != null) {
         if(p != null) {
             stack.push(p);  // Just like recursion
             p = p.left;   
             
         } else {
            TreeNode node = stack.pop();
            if(++count == k) return node.val; 
            p = node.right;
         }
     }
     
     return Integer.MIN_VALUE;
 }

  public int kthSmallest(TreeNode root, int k) {
        int count = countNodes(root.left);
        if (k <= count) {
            return kthSmallest(root.left, k);
        } else if (k > count + 1) {
            return kthSmallest(root.right, k-1-count); // 1 is counted as current node
        }
        
        return root.val;
    }
    
    public int countNodes(TreeNode n) {
        if (n == null) return 0;
        
        return 1 + countNodes(n.left) + countNodes(n.right);
    }

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    private void inOrder(TreeNode root, int[] k) {
        if (root == null) return;
        inOrder(root.left, k);
        if (--k[0] == 0) {
            k[1] = root.val;
        }
        inOrder(root.right, k);
    }
    public int kthSmallest(TreeNode root, int k) {
        int[] res = new int[2];
        res[0] = k;
        inOrder(root, res);
        return res[1];
    }
}