2020 day 10

2020/10/input.txt

@@ -0,0 +1,104 @@
+152
+18
+146
+22
+28
+133
+114
+67
+19
+37
+66
+14
+90
+163
+26
+149
+71
+106
+46
+143
+145
+12
+151
+105
+58
+130
+93
+49
+74
+83
+129
+122
+63
+134
+86
+136
+166
+169
+159
+3
+178
+88
+103
+97
+110
+53
+125
+128
+9
+15
+78
+1
+50
+87
+56
+89
+60
+139
+113
+43
+36
+118
+170
+96
+135
+23
+144
+153
+150
+142
+95
+180
+35
+179
+80
+13
+115
+2
+171
+32
+70
+6
+72
+119
+29
+79
+27
+47
+107
+73
+162
+172
+57
+40
+48
+100
+64
+59
+175
+104
+156
+94
+77
+65

2020/10/part1.js

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+const fs = require('fs');
+const data = fs.readFileSync('input.txt', 'utf-8');
+const lines = data.split('\n').map(num => parseInt(num)).sort((a,b)=>(a-b));
+lines.unshift(0); // add the outlet with joltage 0
+lines.push(lines[lines.length-1]+3); // your device has a joltage 3 above the highest
+let threes = 0; // keep track of differences for puzzle solution
+let ones = 0;
+for (let i = 1; i < lines.length; i++) {
+  switch (lines[i]-lines[i-1]) {
+    case 3:
+      threes++;
+      break;
+    case 1:
+      ones++;
+      break;
+  }
+}
+console.log(ones * threes)

2020/10/part2.js

@@ -0,0 +1,69 @@
+const fs = require('fs');
+const data = fs.readFileSync('input.txt', 'utf-8');
+const lines = data.split('\n').map(num => parseInt(num)).sort((a,b)=>(a-b));
+lines.unshift(0);
+lines.push(lines[lines.length-1]+3);
+
+
+// convert to linked list
+let last = {};
+let i = 0
+do {
+  let entry = {
+    value: lines[i],
+    prev: last
+  };
+  last.next = entry;
+  last = entry;
+  i++;
+} while (i < lines.length)
+
+// find removeable adaptors
+let removeableAdaptors = [];
+const lastVal = last
+last = last.prev
+while (last.prev) {
+  if (last.next.value - last.prev.value <= 3){
+    removeableAdaptors.push(last)
+  }
+  last = last.prev
+}
+
+// divide removeable adaptors into groups that don't interfere with one another when removed
+// this changes the runtime with the given input from a over a month to less than a millisecond
+// however, in a worst case scenareo, where every adaptor is removeable, this would still take trillions of years.
+let adaptorGroups = []
+function makeGroups(removeableAdaptors) {
+  for (let i = removeableAdaptors.length-1; i>-1; i--) {
+    // if the gap between two removeable adaptors > 2 then you know they will not intefere with each other
+    if (i == 0 || removeableAdaptors[i-1].value - removeableAdaptors[i].value > 2) {
+      adaptorGroups.push(removeableAdaptors.slice(i))
+      makeGroups(removeableAdaptors.slice(0, i))
+      break;
+    }
+  }
+}
+makeGroups(removeableAdaptors)
+
+function findArrangements (removeableAdaptors, s = 0) {
+  total = 1
+  // for each adaptor in the group
+  for (let i = s; i < removeableAdaptors.length; i++){
+    // if you can remove this adaptor
+    if (removeableAdaptors[i].next.value-removeableAdaptors[i].prev.value <= 3) {
+      // remove the adaptor and find arrangements with it gone
+      removeableAdaptors[i].prev.next = removeableAdaptors[i].next
+      total += findArrangements (removeableAdaptors, i+1)
+      // add the adaptor back for following tests
+      removeableAdaptors[i].prev.next = removeableAdaptors[i]
+    }
+  }
+  return total
+}
+
+console.time('time')
+// multipy the amount of arrangements in each group to get the total amount of arrangements.
+answer = adaptorGroups.reduce((a, g) => {return a*findArrangements(g)},1)
+console.timeEnd('time')
+
+console.log(answer)

2020/10/test1.txt

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+16
+10
+15
+5
+1
+11
+7
+19
+6
+12
+4

2020/10/test2.txt

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+28
+33
+18
+42
+31
+14
+46
+20
+48
+47
+24
+23
+49
+45
+19
+38
+39
+11
+1
+32
+25
+35
+8
+17
+7
+9
+4
+2
+34
+10
+3

2020/10/worst_scenareo.txt

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+1
+2
+3
+4
+5
+6
+7
+8
+9
+10
+11
+12
+13
+14
+15
+16
+17
+18
+19
+20
+21
+22
+23
+24
+25

README.md

@@ -50,6 +50,7 @@ if (advent) {
 7. [:star: :star:](https://adventofcode.com/2020/day/7 "see puzzle")
 8. [:star: :star:](https://adventofcode.com/2020/day/8 "see puzzle")
 9. [:star: :star:](https://adventofcode.com/2020/day/9 "see puzzle")
+10. [:star: :star:](https://adventofcode.com/2020/day/10 "see puzzle")
 
 ## Languages Used
 * Python