{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)." ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "# Solution Notebook" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Problem: Move all zeroes in a list to the end.\n", "\n", "* [Constraints](#Constraints)\n", "* [Test Cases](#Test-Cases)\n", "* [Algorithm](#Algorithm)\n", "* [Code](#Code)\n", "* [Unit Test](#Unit-Test)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Constraints\n", "\n", "* Is the input an array of ints?\n", " * Yes\n", "* Is the output a new array of ints?\n", " * No, do this in-place\n", "* Do we need to maintain ordering of non-zero values?\n", " * Yes\n", "* Can we assume the inputs are valid?\n", " * No\n", "* Can we assume this fits memory?\n", " * Yes" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Test Cases\n", "\n", "
```\n",
"* None -> TypeError\n",
"* [0, 1, 0, 3, 12] -> [1, 3, 12, 0, 0]\n",
"* [1, 0] -> [1, 0]\n",
"* [0, 1] -> [1, 0]\n",
"* [0] -> [0]\n",
"* [1] -> [1]\n",
"* [1, 1] -> [1, 1]\n",
"```
" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Algorithm\n", "\n", "* pos = 0\n", "* Loop through each item in the input\n", " * If the item != 0, set input[pos] = item\n", " * pos++\n", "* Fill input[pos:] with zeroes\n", "\n", "
```\n",
" |\n",
"[0, 1, 0, 3, 12]\n",
" ^\n",
"    |\n",
"[0, 1, 0, 3, 12]\n",
" ^\n",
"    |\n",
"[1, 1, 0, 3, 12]\n",
" ^\n",
"       |\n",
"[1, 1, 0, 3, 12]\n",
"    ^\n",
"          |\n",
"[1, 1, 0, 3, 12]\n",
"    ^\n",
"          |\n",
"[1, 3, 0, 3, 12]\n",
"    ^\n",
"              |\n",
"[1, 3, 0, 3, 12]\n",
"       ^\n",
"              |\n",
"[1, 3, 12, 3, 12]\n",
"       ^\n",
"\n",
"Fill right with zeroes:\n",
"\n",
"[1, 3, 12, 3, 12]\n",
"           ^\n",
"[1, 3, 12, 0, 12]\n",
"           ^\n",
"[1, 3, 12, 0, 0]\n",
"              ^\n",
"```
\n", "\n", "Complexity:\n", "* Time: O(n)\n", "* Space: O(1)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Code" ] }, { "cell_type": "code", "execution_count": 1, "metadata": {}, "outputs": [], "source": [ "class Solution(object):\n", "\n", " def move_zeroes(self, nums):\n", " if nums is None:\n", " raise TypeError('nums cannot be None')\n", " pos = 0\n", " for num in nums:\n", " if num != 0:\n", " nums[pos] = num\n", " pos += 1\n", " if pos < len(nums):\n", " nums[pos:] = [0] * (len(nums) - pos)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Unit Test" ] }, { "cell_type": "code", "execution_count": 2, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Overwriting test_move_zeroes.py\n" ] } ], "source": [ "%%writefile test_move_zeroes.py\n", "import unittest\n", "\n", "\n", "class TestMoveZeroes(unittest.TestCase):\n", "\n", " def test_move_zeroes(self):\n", " solution = Solution()\n", " self.assertRaises(TypeError, solution.move_zeroes, None)\n", " array = [0, 1, 0, 3, 12]\n", " solution.move_zeroes(array)\n", " self.assertEqual(array, [1, 3, 12, 0, 0])\n", " array = [1, 0]\n", " solution.move_zeroes(array)\n", " self.assertEqual(array, [1, 0])\n", " array = [0, 1]\n", " solution.move_zeroes(array)\n", " self.assertEqual(array, [1, 0])\n", " array = [0]\n", " solution.move_zeroes(array)\n", " self.assertEqual(array, [0])\n", " array = [1]\n", " solution.move_zeroes(array)\n", " self.assertEqual(array, [1])\n", " array = [1, 1]\n", " solution.move_zeroes(array)\n", " self.assertEqual(array, [1, 1])\n", " print('Success: test_move_zeroes')\n", "\n", "\n", "def main():\n", " test = TestMoveZeroes()\n", " test.test_move_zeroes()\n", "\n", "\n", "if __name__ == '__main__':\n", " main()" ] }, { "cell_type": "code", "execution_count": 3, "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Success: test_move_zeroes\n" ] } ], "source": [ "%run -i test_move_zeroes.py" ] } ], "metadata": { "kernelspec": { "display_name": "Python 3", "language": "python", "name": "python3" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 3 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython3", "version": "3.7.2" } }, "nbformat": 4, "nbformat_minor": 1 }