solved day23 part 2

README.md

@@ -108,6 +108,7 @@ For hardness: S(Simple), M(Middle), H(Hard).
 | 20  |   S/M    | find stable/filter collisions   |
 | 21  |   M/M    | iterate grid                    |
 | 22  |   S/S    | infinite grid                   |
+| 23  |   S/H    | cpu/assembly to filter primes   |
 | 24  |   S/S    | dfs                             |
 | 25  |   S/-    | turing machine                  |
 

lib/2017/day23.js

@@ -4,6 +4,14 @@ const rInstr = /(\w+) ([a-h]|-?\d+)(?: ([a-h]|-?\d+))?/;
 let mul = 0;
 
 module.exports = function(part, data) {
+    if (part == 1) {
+        f1(data);
+    } else {
+        f2();
+    }
+};
+
+function f1(data) {
     const instrs = _.map(data.split('\n'), (line) => rInstr.exec(line));
     let ip = 0;
     let regs = {
@@ -21,7 +29,7 @@ module.exports = function(part, data) {
         ip = exec(regs, instrs, ip);
     }
     console.log(mul);
-};
+}
 
 function exec(regs, instrs, ip) {
     const matches = instrs[ip];
@@ -51,3 +59,54 @@ function exec(regs, instrs, ip) {
 function getVal(regs, r) {
     return /[a-z]/.test(r) ? (regs[r] || 0) : parseInt(r);
 }
+
+// Count composite numbers between b and c (include c)
+//
+// set b 65
+// set c b // c = 65
+// jnz a 2
+//         jnz 1 5 // part 1, goto 9 directly
+//     mul b 100
+//     sub b -100000 // b = b * 100 + 100000
+//     set c b
+//     sub c -17000 // c = b + 17000
+// set f 1
+// set d 2
+//     set e 2
+//         set g d
+//         mul g e
+//         sub g b // g = d * e - b
+//         jnz g 2
+//             set f 0
+//         sub e -1 // e++
+//         set g e
+//         sub g b // e - b
+//         jnz g -8
+//     sub d -1 // d++
+//     set g d
+//     sub g b // d - b
+//     jnz g -13
+// jnz f 2
+//     sub h -1 // h++
+// set g b
+// sub g c
+// jnz g 2 // b - c
+//     jnz 1 3
+// sub b -17 // b += 17
+// jnz 1 -23 // goto 9
+function f2() {
+    let b = 65;
+    b = b * 100 + 100000;
+    let c = b + 17000;
+
+    const candidates = _.map(_.range(b, c + 1, 17), (n) => ({n}));
+    for (let i = 2, max = Math.floor(Math.sqrt(c)); i <= max; i++) {
+        _.each(candidates, (item) => {
+            if (item.composite || (item.n % i)) return;
+            item.composite = true;
+        });
+    }
+
+    const count = _.filter(candidates, (item) => item.composite).length;
+    console.log(count);
+}