## Question

Given a binary search tree, print out the elements of the tree in order without using recursion.

eg.

1 2 3 4 5 6 7 |
1 2 3 5 6 7 8 |

Once you think that you’ve solved the problem, click below to see the solution.

*As always, remember that practicing coding interview questions is as much about how you practice as the question itself. Make sure that you give the question a solid go before skipping to the solution. Ideally if you have time, write out the solution first by hand and then only type it into your computer to verify your work once you've verified it manually. To learn more about how to practice, check out this blog post.*

## Solution

How was that problem? You can check out the solution in the video below.

Here is the source code for the solution shown in the video (Github):

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 |
// Tree node class public static class Node { Node left; Node right; int value; public Node(int value) { this.value = value; } } // Traverse tree iteratively. We do this by replicating the same process // done recursively using an explicit stack public static void traverse(Node n) { Stack s = new Stack(); // Add the leftmost branch to the stack addLeftToStack(s, n); // While there are elements in the stack, pop and move the minimum // possible distance to the right while (!s.isEmpty()) { Node curr = s.pop(); System.out.println(curr.value); // Add the right child and any of its left children to the stack addLeftToStack(s, curr.right); } } // As long as the current node has a left pointer, add it to the stack and // continue private static void addLeftToStack(Stack s, Node n) { while (n != null) { s.push(n); n = n.left; } } |

Did you get the right answer to this coding interview question? Please share your thoughts in the comments below.