Zigzag Level Order Traversal in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to initialize the result array for storing levels.

DSA Javascript

function zigzagLevelOrder(root) {
  const [1] = [];
  if (!root) return [];
  // rest of code
}

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Alevels

Bqueue

Cstack

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'queue' instead of 'result' for storing output.

Not initializing an array before use.

We need an array named 'result' to store the nodes level by level in zigzag order.

2fill in blank

medium

Complete the code to add the root node to the queue for BFS traversal.

DSA Javascript

function zigzagLevelOrder(root) {
  const result = [];
  if (!root) return [];
  const queue = [];
  queue.[1](root);
  // rest of code
}

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Apop

Bshift

Cpush

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' or 'shift' which remove elements instead of adding.

Using 'unshift' which adds to the front, not the end.

We add the root node to the end of the queue using 'push' to start BFS.

3fill in blank

hard

Fix the error in the code to toggle the direction for zigzag traversal.

DSA Javascript

let leftToRight = true;
while (queue.length > 0) {
  const levelSize = queue.length;
  const levelNodes = [];
  for (let i = 0; i < levelSize; i++) {
    const node = queue.shift();
    if (leftToRight) {
      levelNodes.push(node.val);
    } else {
      levelNodes.[1](node.val);
    }
    // add children
  }
  result.push(levelNodes);
  leftToRight = !leftToRight;
}

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Aunshift

Bpush

Cshift

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'push' instead of 'unshift' causing wrong order.

Not toggling the direction boolean properly.

To add elements in reverse order, use 'unshift' to add at the front of the array.

4fill in blank

hard

Fill both blanks to add left and right children to the queue if they exist.

DSA Javascript

for (let i = 0; i < levelSize; i++) {
  const node = queue.shift();
  if (node.[1]) queue.push(node.[1]);
  if (node.[2]) queue.push(node.[2]);
}

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Aleft

Bright

Cval

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'val' or 'parent' instead of 'left' or 'right'.

Not checking if child exists before pushing.

We add 'left' and 'right' children nodes to the queue if they exist.

5fill in blank

hard

Fill all three blanks to complete the zigzag level order traversal function.

DSA Javascript

function zigzagLevelOrder(root) {
  if (!root) return [];
  const result = [];
  const queue = [root];
  let leftToRight = true;
  while (queue.length > 0) {
    const levelSize = queue.length;
    const levelNodes = [];
    for (let i = 0; i < levelSize; i++) {
      const node = queue.[1]();
      if (leftToRight) {
        levelNodes.push(node.val);
      } else {
        levelNodes.[2](node.val);
      }
      if (node.left) queue.push(node.[3]);
      if (node.right) queue.push(node.right);
    }
    result.push(levelNodes);
    leftToRight = !leftToRight;
  }
  return result;
}

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Ashift

Bunshift

Cleft

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' instead of 'shift' breaks BFS order.

Using 'push' instead of 'unshift' for reverse order.

Using wrong child property name.

We remove nodes from the front with 'shift', add reversed order with 'unshift', and add left child with 'left'.