Add Day 10 2020

src/2020/day10/input

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+8
+131
+91
+35
+47
+116
+105
+121
+56
+62
+94
+72
+13
+82
+156
+102
+12
+59
+31
+138
+46
+120
+7
+127
+126
+111
+2
+123
+22
+69
+18
+157
+75
+149
+88
+81
+23
+98
+132
+1
+63
+142
+37
+133
+61
+112
+122
+128
+155
+145
+139
+66
+42
+134
+24
+60
+9
+28
+17
+29
+101
+148
+96
+68
+25
+19
+6
+67
+113
+55
+40
+135
+97
+79
+48
+159
+14
+43
+86
+36
+41
+85
+87
+119
+30
+108
+80
+152
+158
+151
+32
+78
+150
+95
+3
+52
+49

src/2020/day10/part1.ts

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+export const part1 = (input: string) => {
+  const joltage = [0, ...input.split('\n')].map(Number).sort((a, b) => a - b);
+
+  let oneDiff = 0;
+  let threeDiff = 1; // 3 higher than the highest-rated adapter.
+
+  joltage.forEach((current, i) => {
+    const diff = joltage[i + 1] - current;
+    if (diff === 1) oneDiff++;
+    else if (diff === 3) threeDiff++;
+  });
+
+  return oneDiff * threeDiff;
+};

src/2020/day10/part2.ts

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+const countDistinctWays = (input: number[]) => {
+  const lastIndex = input.length - 1;
+  const distinctWays = input.reduce(
+    (distinctWays, adapter, i) => {
+      // Compare current adapter with the three next neighbours and
+      // check if the joltage difference less or equal to three.
+      for (let j = i + 1; j < i + 4; j++) {
+        if (input[j] - adapter <= 3) {
+          distinctWays[j] += distinctWays[i];
+        }
+      }
+      return distinctWays;
+    },
+    [1, ...Array(lastIndex).fill(0)] // First is always valid
+  );
+  return distinctWays[lastIndex];
+};
+
+export const part2 = (input: string) => {
+  const adapters = [0, ...input.split('\n')].map(Number).sort((a, b) => a - b);
+  adapters.push(adapters[adapters.length - 1] + 3); // 3 higher than the highest-rated adapter.
+
+  return countDistinctWays(adapters);
+};

src/2020/day10/test.spec.ts

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+import {readInput} from '../../utils';
+
+import {part1} from './part1';
+import {part2} from './part2';
+
+describe('Advent of Code 2020 - Day 10', () => {
+  let input: string;
+  let testInput: string;
+
+  beforeAll(async () => {
+    input = await readInput(__dirname + '/input');
+    testInput = await readInput(__dirname + '/test_input');
+  });
+
+  describe('part 1', () => {
+    it('should output 7*5', () => {
+      const input = `16
+10
+15
+5
+1
+11
+7
+19
+6
+12
+4`;
+      expect(part1(input)).toBe(7 * 5);
+    });
+    it('should output 22*10 ', () => {
+      expect(part1(testInput)).toBe(22 * 10);
+    });
+
+    it('should output 2112 from input', () => {
+      expect(part1(input)).toBe(2112);
+    });
+  });
+
+  describe('part 2', () => {
+    it('should output 8', () => {
+      const input = `16
+10
+15
+5
+1
+11
+7
+19
+6
+12
+4`;
+      expect(part2(input)).toBe(8);
+    });
+
+    it('should output 19208 ', () => {
+      expect(part2(testInput)).toBe(19208);
+    });
+
+    it('should output 3022415986688 from input', () => {
+      expect(part2(input)).toBe(3022415986688);
+    });
+  });
+});

src/2020/day10/test_input

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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