AoC

Author: norvig

ipynb/Advent-2022.ipynb

@@ -1778,7 +1778,9 @@
    "source": [
     "#### Part 1: Determine which pairs of packets are already in the right order. What is the sum of the indices of those pairs?\n",
     "\n",
-    "The notion of \"right order\" is almost the same as \"less than\", except that an integer is equal to a singleton list. Also, I was confused for a bit because the rules don't say whether two identical lists are in the right order or not; the rules just say you should \"continue checking\" in that case. I decided that I should not define a Boolean truth predicate; rather it should be a *ternary* comparison function. By convention, a Python comparison function, `compare(left, right)`, returns a negative number if `left < right`, zero if they are equal, and a positive number if `left > right`. I'll implement that:"
+    "The notion of \"right order\" is almost the same as \"less than\", except that an integer can match against a singleton list. Also, I was confused for a bit because the rules don't say whether two identical lists are in the right order or not; the rules just say you should \"continue checking\" in that case. I decided that I should not define a Boolean truth predicate; rather it should be a *ternary* comparison function. \n",
+    "\n",
+    "By convention, a Python comparison function, `compare(left, right)`, returns a negative number if `left < right`, zero if they are equal, and a positive number if `left > right`. I'll implement that:"
    ]
   },
   {
@@ -1791,18 +1793,18 @@
     "    \"\"\"Are the two packets in the right order? \n",
     "    Negative number for right order; 0 for equal; positive for wrong order.\"\"\"\n",
     "    types = (type(left), type(right))\n",
-    "    if   types == (int,  int):   return left - right\n",
-    "    elif types == (int,  list):  return compare([left], right)\n",
-    "    elif types == (list, int):   return compare(left, [right])\n",
-    "    elif types == (list, list):  return first_true(map(compare, left, right), \n",
-    "                                                   default=len(left) - len(right))"
+    "    if   types == (int,  int):  return left - right\n",
+    "    elif types == (int,  list): return compare([left], right)\n",
+    "    elif types == (list, int):  return compare(left, [right])\n",
+    "    elif types == (list, list): return first_true(map(compare, left, right), \n",
+    "                                                  default=len(left) - len(right))"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "The call to `first_true` (from my [AdventUtils](AdventUtils.ipynb) or from [itertools recipes](https://docs.python.org/3/library/itertools.html#itertools-recipes)) says to `compare` respective successive elements of the two lists one by one, and to return the first true (i.e. non-zero) comparison, or if one of the two lists is exhausted first,  return the comparison of the list lengths. \n",
+    "The call to `first_true` (from my [AdventUtils](AdventUtils.ipynb)) says to `compare` respective successive elements of the two lists one by one, and to return the first truthy (i.e. non-zero) comparison, or if one of the two lists is exhausted first,  return the comparison of the list lengths. \n",
     "\n",
     "I threw in some test cases to gain some confidence that I got it right: "
    ]
@@ -1850,9 +1852,9 @@
    "source": [
     "#### Part 2: Organize all of the packets into the correct order. What is the decoder key for the distress signal?\n",
     "\n",
-    "This should be easy; all I have to do is sort using `right_order`, then look up the resulting indices of the two divider packets (taking care to use 1-based rather than 0-based indexing). I tried to sort using `key=right_order` and got an error message reminding me how foolish I am: `right_order` is not a key function (of one argument), it is a comparison function (of two arguments).\n",
+    "This should be easy; all I have to do is sort using `compare`, then look up the resulting indices of the two divider packets (taking care to use 1-based rather than 0-based indexing). I tried to sort using `key=compare` and got an error message reminding me how foolish I am: `compare` is not a key function (of one argument), it is a comparison function (of two arguments).\n",
     "\n",
-    "In Python 2, the `sorted` function did accept a two-argument `cmp` function, but in Python 3 that functionality is gone. I had to look it up to find that the `functools.cmp_to_key` function converts a comparison function to a key function, and that a `cmp_to_key` comparison function returns -1/0/+1, not True/None/False like my `right_order` does. Once I correct for that, it works fine."
+    "In Python 2, the `sorted` function accepted a two-argument `cmp` function, but in Python 3 that functionality is gone. I had to look it up to find that the `functools.cmp_to_key` function converts a comparison function to a key function. "
    ]
   },
   {