2020 day 9

2020/09/part1.js

@@ -0,0 +1,21 @@
+const fs = require('fs');
+const data = fs.readFileSync('input.txt', 'utf-8');
+const lines = data.split('\n').map(num => parseInt(num));
+const preambleLength = 25;
+
+let first
+for (let i = preambleLength; i < lines.length; i++) {
+  valid = false
+  for (let j = i-preambleLength; j < i && !valid; j++) {
+    for (let k = j+1; k < i && !valid; k++) {
+      if (lines[j]+lines[k]== lines[i]) {
+        valid = true
+      }
+    }
+  }
+  if (!valid) {
+    first = lines[i]
+    break
+  }
+}
+console.log(first)

2020/09/part2.js

@@ -0,0 +1,30 @@
+const fs = require('fs');
+const data = fs.readFileSync('input.txt', 'utf-8');
+const lines = data.split('\n').map(num => parseInt(num));
+const preambleLength = 25;
+
+let sum
+for (let i = preambleLength; i < lines.length; i++) {
+  valid = false
+  for (let j = i-preambleLength; j < i && !valid; j++) {
+    for (let k = j+1; k < i && !valid; k++) {
+      if (lines[j]+lines[k]== lines[i]) {
+        valid = true
+      }
+    }
+  }
+  if (!valid) {
+    sum = lines[i]
+    break
+  }
+}
+
+for ( let start = 0; start < lines.length; start++) {
+  for (let end = start+1; end < lines.length; end++) {
+    if (lines[end] > sum) {continue}
+    let range = lines.slice(start, end)
+    if (range.reduce((a,b) => (a+b)) == sum) {
+      console.log(Math.min(...range)+ Math.max(...range))
+    }
+  }
+}

README.md

@@ -49,6 +49,7 @@ if (advent) {
 6. [:star: :star:](https://adventofcode.com/2020/day/6 "see puzzle")
 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")
 
 ## Languages Used
 * Python