Day 25

Author: monk-time

2017/aoc25.js

@@ -0,0 +1,26 @@
+'use strict';
+
+{
+    const op = (value, dir, state) => (tape, i) => {
+        tape[i] = value;
+        return [state, i + dir];
+    };
+
+    const execute = (rules, state, steps, i = 0) => {
+        const tape = {};
+        while (steps--) [state, i] = rules[`${state}${tape[i] || 0}`](tape, i);
+        return Object.values(tape).reduce((a, b) => a + b);
+    };
+
+    const input = document.body.textContent.trim().split('\n\n');
+    const [, state0, steps] = input[0].match(/state ([A-Z])\.\n.+?(\d+)/);
+    const reOp = /[A-Z](?=[.:])|[01]|left|right/;
+    const rules = input.slice(1).map(p => p.split('\n').map(s => s.match(reOp)[0]))
+        .reduce((acc, [st, , v0, d0, st0, , v1, d1, st1]) => ({
+            ...acc,
+            [`${st}0`]: op(+v0, d0 === 'left' ? -1 : 1, st0),
+            [`${st}1`]: op(+v1, d1 === 'left' ? -1 : 1, st1),
+        }), {});
+
+    console.log(execute(rules, state0, +steps));
+}

scraps.js

@@ -21,6 +21,13 @@ browser console on the /input page (F12 → Console):
     const getGrid = n => new Array(n).fill().map(() => new Array(n).fill(0));
     const getGrid2 = n => [...new Array(n)].map(() => new Array(n).fill(0));
 
+    // Timed execution
+    (f => { console.time('main'); f(); console.timeEnd('main'); })(() => { // eslint-disable-line
+    });
+
+    // Timed execution for Promises
+    const timed = f => () => { console.time('main'); f(); console.timeEnd('main'); }; // eslint-disable-line
+
     // Generate and draw infinite grid from an odd-sized center segment
     const halfWidth = Math.floor(input[0].length / 2);
     const key = (i, j) => `${i},${j}`;
@@ -47,13 +54,6 @@ browser console on the /input page (F12 → Console):
         return a.map(row => row.join('').replace(/\] | {2}| \[/g, s => s.trim() || ' ')).join('\n');
     };
 
-    // Timed execution
-    (f => { console.time('main'); f(); console.timeEnd('main'); })(() => { // eslint-disable-line
-    });
-
-    // Timed execution for Promises
-    const timed = f => () => { console.time('main'); f(); console.timeEnd('main'); }; // eslint-disable-line
-
     // Permutation generator and minmax tracker (separate)
     const permute = function* (arr, used = []) {
         if (arr.length === 0) yield [...used];