task 4.js

const ids = `51-88,52-87
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34-47,17-33
7-66,7-89
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40-41,18-40
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57-86,51-61
66-68,62-67
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8-85,7-62
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52-72,29-53
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15-54,16-36
3-96,4-95
13-14,16-87
22-41,39-42
60-65,59-59
74-80,15-74
61-61,4-60
38-84,39-84
6-16,6-6
1-96,96-97
1-98,97-98
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8-86,7-7
12-97,4-97
81-88,80-88
8-82,6-6
94-96,3-95
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53-92,75-85
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39-53,8-53
10-67,9-66
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38-53,27-60
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1-1,9-64
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62-90,88-88
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42-88,42-52
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49-78,50-67
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56-99,98-98
45-96,19-95
48-65,49-66
59-88,90-91
43-78,20-20
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70-76,67-70
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76-98,75-77
34-56,34-56
70-86,85-86
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4-33,1-33
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5-59,3-5
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3-91,3-91
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39-80,38-87
62-63,52-62
1-52,2-52
97-97,2-97
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13-41,13-84
3-42,3-42
70-94,69-93
16-53,15-52
90-96,13-57
63-75,60-76
87-87,4-55
3-44,4-85
7-98,10-87
2-65,3-65
27-93,27-92
35-54,34-53
40-75,98-99
14-14,13-53
16-16,17-97
39-96,41-96
70-72,71-97
35-35,32-36
48-84,85-95
7-81,11-81
31-94,31-94
1-2,4-72
3-99,3-99
92-94,21-28
39-73,38-83
6-57,6-57
68-90,67-98
9-81,10-82
57-81,57-81
16-59,57-60
10-42,2-43
14-77,12-15
88-88,3-87
88-89,13-89
68-69,7-69
63-92,92-98
37-87,85-86
4-56,5-22
15-52,51-51
92-93,74-92
9-98,7-10
17-17,18-53
55-88,61-72
38-81,65-78
98-99,59-73
17-22,18-22
69-94,68-69
84-85,6-84
12-12,13-95
8-34,7-8
2-38,3-38
20-29,28-80
21-52,22-52
36-91,90-92
5-90,4-91
1-41,1-36
3-76,10-98
14-41,2-14
18-64,19-64
37-93,83-92
31-36,32-60
53-83,47-84
2-89,70-77
28-83,84-84
31-59,58-71
10-98,10-87
19-80,20-81
11-17,9-18
29-76,48-52
10-33,33-65
20-83,68-99
14-43,13-13
44-71,62-70
59-63,49-64
14-94,94-95
5-89,2-2
83-95,84-95
2-9,8-93
63-69,68-68
73-75,5-74
82-92,91-93
5-5,4-57
35-39,35-83
71-83,56-83
87-87,8-88
95-98,2-30
10-60,59-89
13-23,25-93
73-86,22-85
32-47,46-90
5-79,3-16
20-92,28-69
30-31,19-31
41-70,9-36
1-49,2-98
1-96,41-96
44-50,44-71
1-28,2-27
13-93,74-92
37-38,31-37
4-79,3-80
14-50,37-37
5-68,46-68
23-63,22-63
3-94,1-3`;

// part 1

// returns true if any pair fully contains seconds one
const pairs_overlap_checker = (pairs) => {
  const [pair1, pair2] = pairs.split(",");
  const [pair1_start, pair1_end] = pair1.split("-");
  const [pair2_start, pair2_end] = pair2.split("-");
  if (+pair1_start <= +pair2_start && +pair1_end >= +pair2_end) return true; // pair 1 contains pair 2
  if (+pair1_start >= +pair2_start && +pair1_end <= +pair2_end) return true; // pair 2 contains pair 1
  return false;
};

console.assert(
  pairs_overlap_checker("2-8,3-7") == true,
  "For example, 2-8 fully contains 3-7"
);
console.assert(
  pairs_overlap_checker("6-6,4-6") == true,
  "and 6-6 is fully contained by 4-6"
);

const test_ids = `2-4,6-8
2-3,4-5
5-7,7-9
2-8,3-7
6-6,4-6
2-6,4-8`;

console.assert(
  test_ids
    .split("\n")
    .map(pairs_overlap_checker)
    .reduce((a, c) => +a + +c, 0) == 2,
  "In pairs where one assignment fully contains the other, one Elf in the pair would be exclusively cleaning sections their partner will already be cleaning, so these seem like the most in need of reconsideration. In this example, there are 2 such pairs"
);

// solution for 1st part
console.table({
  "result 1": ids
    .split("\n")
    .map(pairs_overlap_checker)
    .reduce((a, c) => +a + +c, 0),
});

// part 2

// returns true if there any overlap
const pairs_any_overlap_checker = (pairs) => {
  const [pair1, pair2] = pairs.split(",");
  const [pair1_start, pair1_end] = pair1.split("-");
  const [pair2_start, pair2_end] = pair2.split("-");

  if (+pair1_start < +pair2_start && +pair1_end < +pair2_start) return false; // every number in pair 1 is smaller than smallest from pair 2
  if (+pair1_start > +pair2_end && +pair1_end > +pair2_end) return false; // every number in pair 1 is bigger than biggest from pair 2
  return true;
};

console.assert(
  pairs_any_overlap_checker("5-7,7-9") == true,
  "5-7,7-9 overlaps in a single section, 7."
);
console.assert(
  pairs_any_overlap_checker("2-8,3-7") == true,
  "2-8,3-7 overlaps all of the sections 3 through 7"
);
console.assert(
  pairs_any_overlap_checker("6-6,4-6") == true,
  "6-6,4-6 overlaps in a single section, 6"
);
console.assert(
  pairs_any_overlap_checker("2-6,4-8") == true,
  "2-6,4-8 overlaps in sections 4, 5, and 6."
);

console.assert(
  test_ids
    .split("\n")
    .map(pairs_any_overlap_checker)
    .reduce((a, c) => +a + +c, 0) == 4,
  "So, in this example, the number of overlapping assignment pairs is 4."
);

// solution for 2nd part
console.table({
  "result 2": ids
    .split("\n")
    .map(pairs_any_overlap_checker)
    .reduce((a, c) => +a + +c, 0),
});