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#117 - Populating Next Right Pointers in Each Node II

Medium • View on LeetCode • View on GitHub

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

Problem Description

Given a binary tree, 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) {
  if (root === null) return root;

  const depth = 0;
  const stack = [[root, depth]];

  while (stack.length) {
    const [node, depth] = stack.shift();
    if (stack.length) {
      const [nextNode, nextDepth] = stack[0];
      if (depth === nextDepth) {
        node.next = nextNode;
      }
    }
    if (node.left) {
      stack.push([node.left, depth + 1]);
    }
    if (node.right) {
      stack.push([node.right, depth + 1]);
    }
  }

  return root;
};

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