make d14p2 better

day14/d14p2.swift

@@ -35,31 +35,43 @@ func readInput(_ filePath: String) throws -> [Robot] {
     return robots
 }
 
-func complexity(_ input: String) -> Int {
-    var last: Character = " "
-    return input.reduce(0, { s, c in
-        if c != last { last = c; return s + 1 } else { return s }
-    })
+func variance(_ bots: [Robot]) -> Int {
+    let (sX, sY) = bots.reduce((0, 0)) { s, bot in (s.0 + bot.x, s.1 + bot.y) }
+    let (mX, mY) = (sX/bots.count, sY/bots.count)
+    return bots.reduce(0) { s, bot in
+        s + (mX-bot.x)*(mX-bot.x) + (mY-bot.y)*(mY-bot.y) }
 }
 
-func printRobots(_ robots: [Robot]) -> String {
-    var screen: [[String]] = Array(repeating: Array(repeating: " ", count: 101), count: 103)
-    robots.forEach { robot in screen[robot.y][robot.x] = "█" }
+func printRobots(_ bots: [Robot]) -> String {
+    var screen: [[String]] = Array(
+        repeating: Array(repeating: " ", count: 101),
+        count: 52
+    )
+    bots.forEach { bot in
+        let (q, r) = bot.y.quotientAndRemainder(dividingBy: 2)
+        if screen[q][bot.x] == " " {
+            screen[q][bot.x] = (r == 0) ? "▀" : "▄"
+        } else {
+            screen[q][bot.x] = "█"
+        }
+    }
     return screen.map { row in row.joined() }.joined(separator: "\n")
 }
 
 var bots = try readInput(CommandLine.arguments[1])
 var i = 0
+var minSigma = Int.max
 while true {
     i += 1
     for i in 0..<bots.count {
         bots[i].move()
     }
     let printout = printRobots(bots)
-    let cpx = complexity(printout)
-    if cpx < 800 {
+    let sigma = variance(bots)
+    if sigma < minSigma {
+        minSigma = sigma
+        //print("\u{001B}[2J")
         print(printout)
-        print("i=\(i) rle=\(cpx)")
-        break
+        print("i=\(i) s²=\(sigma)")
     }
 }