Finished day 5

AdventOfCode2018/5thDay/challenge1/index.js

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+const day4 = require('./istolethisfromsomeone');
+const fs = require('fs');
+
+console.log('Part 1: ' + day4.part1(fs.readFileSync('input.txt').toString()));
+console.log('Part 2: ' + day4.part2(fs.readFileSync('input.txt').toString()));

AdventOfCode2018/5thDay/challenge1/istolethisfromsomeone.js

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+function part1(data) {
+    const polymer = data.split("");
+    const removeChar = ""; // No removal
+    const stack = collapsePloymer(polymer, removeChar);
+    return stack.length;
+}
+
+function collapsePloymer(ploymerChars, removeChar) {
+    const stack = [];
+    for (let i = 0; i < ploymerChars.length; i++) {
+        const char = ploymerChars[i];
+        if (char.toLowerCase() === removeChar.toLowerCase()) {
+            continue;
+        }
+        const last = stack.pop();
+        if (!last) {
+            stack.push(char);
+            continue;
+        }
+        if (last.toLowerCase() === char.toLowerCase() && last !== char) {
+            continue;
+        }
+        stack.push(last);
+        stack.push(char);
+    }
+    return stack;
+}
+
+function part2(data) {
+    const polymer = data.split("");
+    const alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".split("");
+    const collapsedPolymers = alphabet.map(letter =>
+        collapsePloymer(polymer, letter)
+    );
+    const shortestCollapse = collapsedPolymers.reduce((longest, curr) =>
+        longest.length < curr.length ? longest : curr
+    );
+    return shortestCollapse.length;
+}
+
+module.exports = {
+    part1: part1,
+    part2: part2
+};