#314 - Binary Tree Vertical Order Traversal

Medium • View on LeetCode • View on GitHub

Hash Table Sorting Depth-First Search Tree Breadth-First Search Binary Tree

Problem Description

Given the root of a binary tree, return the vertical order traversal of its nodes' values.

(i.e., from top to bottom, column by column).

If two nodes are in the same row and column, the order should be from left to right.

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var verticalOrder = function(root) {
  if (!root) return [];

  const columns = new Map();
  const queue = [[root, 0]];
  let minCol = 0;
  let maxCol = 0;

  while (queue.length) {
    const [node, col] = queue.shift();
    if (!columns.has(col)) columns.set(col, []);
    columns.get(col).push(node.val);

    if (node.left) {
      queue.push([node.left, col - 1]);
      minCol = Math.min(minCol, col - 1);
    }
    if (node.right) {
      queue.push([node.right, col + 1]);
      maxCol = Math.max(maxCol, col + 1);
    }
  }

  const result = [];
  for (let col = minCol; col <= maxCol; col++) {
    if (columns.has(col)) result.push(columns.get(col));
  }

  return result;
};