117. Populating Next Right Pointers in Each Node II

https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii

Python

from collections import defaultdict

class Solution:
    def __init__(self):
        self.map = defaultdict(list)

    def connect(self, root: 'Node') -> 'Node':
        if root is None:
            return root
        self._travel(root.left, 1)
        self._travel(root.right, 1)

        for level in self.map:
            reduce(self._link_nodes, self.map[level])
        return root

    def _link_nodes(self, node1, node2):
        node1.next = node2
        return node2

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

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

Javascript

var connect = function(root) {
  const queue = [];
  if (root) queue.push(root);
  
  while (queue.length) {
    const total = queue.length;
    for (let i = 0; i < total; i++) {
      const node = queue.shift();
      if (i < total - 1) node.next = queue[0];
    
      if (node.left) queue.push(node.left);
      if (node.right) queue.push(node.right);  
    }
    
  }
  return root;
};