Amazon Interview Question for SDE1s

Country: United States

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use stack to push root initially. Then iterate the stack until empty, pop out top and push child starting from right.

void preOrder(Node *root) {

    std::stack<Node *> S;

    while(!S.empty()) {
        Node *temp =;
        std::cout << temp->val << " ";
        for(int i = temp->child.size(); I >=0; i--) {

- vikalpveer March 31, 2018 | Flag Reply
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of 0 vote

Very similar to binary tree traversal but use an array of children as opposed to left and right. Complete solution in Python:

Recursive Solution in Python:

def preOrderRecursive(root):
  res = []
  def helper(root, res):
    if not root:

    for child in root.children:
      helper(child, res)

  helper(root, res)
  return res

Iterative Solution in Python:

def preOrderIterative(root):
  st = []
  res = []
  while len(st):
    curr = st.pop()
    for child in reversed(curr.children):
  return res

Test Code:

class Node:
  def __init__(self, val):
    self.val = val
    self.children = []

Construct the following tree:
          / | \
        2   3  6
            /\  \
            4 5  7
root = Node(1)
root.children = [Node(2), Node(3), Node(6)]
root.children[1].children = [Node(4), Node(5)]
root.children[2].children = [Node(7)]

print(preOrderRecursive(root)) # Output: [1, 2, 3, 4, 5, 6, 7]
print(preOrderIterative(root)) # Output: [1, 2, 3, 4, 5, 6, 7]

- prudent_programmer April 02, 2018 | Flag Reply

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