Given a matrix, return all elements of the matrix in diagonal order.\n\n**Example 1:**\n```\nInput: [[ 1,  2,  3,  4],\n        [ 6,  7,  8,  9],\n        [11, 12, 13, 14],\n        [16, 17, 18, 19]]\n\nOutput: [1, 6, 2, 11, 7, 3, 16, 12, 8, 4, 17, 13, 9, 18, 14, 19]\nExplanation:\n```\n![](https://i.imgur.com/lEKJJhY.png)\n\n**Example 2:**\n```\nInput: [[1, 2, 3],\n        [4, 5, 6],\n        [7, 8, 9]]\n\nOutput: [1, 4, 2, 7, 5, 3, 8, 6, 9]\n```\n\n-------------------------------------------------------------\n\n**Follow-up:**\nWhat if the input is a [jugged array](https://en.wikipedia.org/wiki/Jagged_array) (rows have different column sizes)?\n\n**Example:**\n```\nInput: [[1, 2, 3, 4],\n        [5         ],\n        [6, 7      ],\n        [8, 9, 0   ]]\n\nOutput: [1, 5, 2, 6, 3, 8, 7, 4, 9, 0]\n```\n\n\nRelated problems:\n* https://leetcode.com/problems/diagonal-traverse/

Given a matrix, return all elements of the matrix in diagonal order.\n\nExample 1:\n\nInput: [[ 1,  2,  3,  4],\n        [ 6,  7,  8,  9],\n        [11, 12, 13,