Week2 HW solutions

gistfile1.txt

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  {
   "cells": [
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "def volume(r):\n    return 2.0/3.0 * 3.141592 * r**3\n\nvolume(5)",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 4,
       "text": "261.7993333333333"
      }
     ],
     "prompt_number": 4
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "def triple(x):\n    new_x = []\n    for j in x:\n        new_x.append(j)\n        new_x.append(j)\n        new_x.append(j)\n    return new_x\n\ntriple([3,4,5])",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 5,
       "text": "[3, 3, 3, 4, 4, 4, 5, 5, 5]"
      }
     ],
     "prompt_number": 5
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "# note, you could also write 'triple' like this:\ndef triple2(x):\n    new_x = []\n    for j in x:\n        new_x.extend([j]*3)\n    return new_x\n\ntriple2([3,4,5])",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 6,
       "text": "[3, 3, 3, 4, 4, 4, 5, 5, 5]"
      }
     ],
     "prompt_number": 6
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "def uniq(x):\n    uniq_x = []\n    for j in x:\n        if not (j in uniq_x):\n            uniq_x.append(j)\n    return uniq_x\n\nuniq([3,4,4,4,4,4])\n",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 7,
       "text": "[3, 4]"
      }
     ],
     "prompt_number": 7
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "def uniq_nocase(x):\n    uniq_x = []\n    for j in x:\n        j = j.lower()\n        if not (j in uniq_x):\n            uniq_x.append(j)\n            \n    return uniq_x\n\nuniq_nocase(['foo', 'Foo'])",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 8,
       "text": "['foo']"
      }
     ],
     "prompt_number": 8
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "# to put the primes in a list, you just need the tagged lines:\n\ndef primes(N):\n    primes_list = []   ## this one\n    num = 2\n    while num < N:\n        is_prime = True\n        trial = 2\n        while trial**2 <= num:\n            if num % trial == 0:\n                is_prime = False\n                break\n            trial += 1\n        \n        if is_prime:\n            primes_list.append(num)   ### this one\n        num += 1\n\n    return primes_list   ### and this one\n\nprimes(10)",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 2,
       "text": "[2, 3, 5, 7]"
      }
     ],
     "prompt_number": 2
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "## for the prime number sieve, you want to replace the middle loop with one that goes through all the primes collected\n## so far and check them to see if they divide the prime number you are testing.\n##\n## I don't think I defined the problem very clearly -- sorry!\n\ndef primes(N):\n    primes_list = []\n    num = 2\n    while num < N:\n        is_prime = True\n        \n        ## start here\n        for r in primes_list:\n            if num % r == 0:\n                is_prime = False\n                break\n        \n        if is_prime:\n            primes_list.append(num)\n        num += 1\n\n    return primes_list\n\nprimes(10)",
     "language": "python",
     "metadata": {},
     "outputs": [
      {
       "output_type": "pyout",
       "prompt_number": 3,
       "text": "[2, 3, 5, 7]"
      }
     ],
     "prompt_number": 3
    },
    {
     "cell_type": "code",
     "collapsed": false,
     "input": "",
     "language": "python",
     "metadata": {},
     "outputs": []
    }
   ],
   "metadata": {}
  }
 ]
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