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102. Binary Tree Level Order Traversal

https://leetcode.com/problems/binary-tree-level-order-traversal

Python​

class Solution:
    def levelOrder(self, root: Optional[TreeNode]) -> List[List[int]]:
        return self._travel([], 0, root)

    def _travel(self, result, level, node):
        if not node:
            return result

        if len(result) < level+1:
            result.append([])

        result[level].append(node.val)
        self._travel(result, level+1, node.left)
        self._travel(result, level+1, node.right)

        return result

Javascript​

var levelOrder = function(root) {
  const queue = [];
  const res = [];  
  let level = 0;
  
  if (root) queue.push(root);
  
  while (queue.length) {
    const total = queue.length;
    res.push([]);
    
    for (let i = 0; i < total; i++) {
      const currNode = queue.shift();    
      res[level].push(currNode.val);
    
      if (currNode.left) queue.push(currNode.left);
      if (currNode.right) queue.push(currNode.right);
    }
    level += 1;
  }
  return res;
};