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#116 - Populating Next Right Pointers in Each Node

Medium • View on LeetCode • View on GitHub

Depth-First Search Tree Breadth-First Search Binary Tree Linked List

Problem Description

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition: Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.

Initially, all next pointers are set to NULL.

Solution

/**
 * // Definition for a Node.
 * function Node(val, left, right, next) {
 *    this.val = val === undefined ? null : val;
 *    this.left = left === undefined ? null : left;
 *    this.right = right === undefined ? null : right;
 *    this.next = next === undefined ? null : next;
 * };
 */

/**
 * @param {Node} root
 * @return {Node}
 */
var connect = function(root) {
  const order = [];
  traverse(order, root);
  for (let level of order) {
    for (let i = 0; i < level.length - 1; i++) {
      level[i].next = level[i + 1];
    }
  }
  return root;
};

function traverse(order, node, level = 0) {
  if (!node) {
    return [];
  }

  order[level] = order[level] || [];
  order[level].push(node);

  traverse(order, node.left, level + 1);
  traverse(order, node.right, level + 1);
}

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