Solve 2020/15

2020/15/solution1.js

@@ -0,0 +1,36 @@
+const input = "9,3,1,0,8,4";
+
+const start = input.split(",");
+const memory = {};
+
+let turn = 1;
+let lastNum = null;
+
+for (const num of start) {
+  if (lastNum !== null) {
+    memory[lastNum] = turn - 1;
+  }
+  lastNum = num;
+  console.log(`Turn ${turn}: ${num}`);
+  turn += 1;
+}
+
+let num;
+while (turn <= 2020) {
+  if (typeof memory[lastNum] === "undefined") {
+    num = 0;
+  } else {
+    num = turn - 1 - memory[lastNum];
+  }
+
+  console.log(
+    `Turn ${turn}: ${num}${
+      num !== 0 ? ` (${turn - 1} - ${memory[lastNum]})` : ""
+    }`
+  );
+  memory[lastNum] = turn - 1;
+  lastNum = num;
+  turn += 1;
+}
+
+console.log("Solution:", num);

2020/15/solution2.js

@@ -0,0 +1,41 @@
+// TODO: optimization needed
+
+// const input = "0,3,6";
+const input = "9,3,1,0,8,4";
+
+const start = input.split(",");
+const memory = {};
+
+let turn = 1;
+let lastNum = null;
+
+for (const num of start) {
+  if (lastNum !== null) {
+    memory[lastNum] = turn - 1;
+  }
+  lastNum = num;
+  console.log(`Turn ${turn}: ${num}`);
+  turn += 1;
+}
+
+let num;
+let lastLog = new Date();
+while (turn <= 30000000) {
+  if (typeof memory[lastNum] === "undefined") {
+    num = 0;
+  } else {
+    num = turn - 1 - memory[lastNum];
+  }
+
+  const now = new Date();
+  if (now - lastLog > 5000) {
+    console.log(`Turn ${turn.toLocaleString()}, num: ${num}`);
+    lastLog = now;
+  }
+
+  memory[lastNum] = turn - 1;
+  lastNum = num;
+  turn += 1;
+}
+
+console.log("Solution:", num);