First optimizations

This gets runtime down to about a quarter of what it was. I need to see if I can apply bisect to the X value, but I'm not sure I understand how/if that can work.

days/19.go

@@ -89,34 +89,34 @@ func (d *Day19) Part2() string {
 		}
 	}
 
-	done := false
-	for y := startY; !done; y++ {
+	lastGoodX := 0
+	threshold := 1
+	y := u.Bisect(startY+100, 9999, threshold, func(y int) bool {
 		foundX := false
 		for x := startX; ; x++ {
 			if !f(x, y) {
 				if !foundX {
 					continue
 				} else {
-					break
+					return true
 				}
 			}
 			if !foundX {
 				foundX = true
-				startX = x
 			}
 
 			if !f(x+99, y) {
-				break
+				return true
 			}
 			if !f(x, y+99) {
 				continue
 			}
 
-			fmt.Printf("x=%d, y=%d, so result=%d\n", x, y, (x*10000)+y)
-			done = true
-			break
+			lastGoodX = x
+			return false
 		}
-	}
+	})
 
-	return "0"
+	result := (lastGoodX * 10000) + y
+	return fmt.Sprintf("Closest 100x100 square for the ship starts at %d,%d = %s%d%s", lastGoodX, y, u.TextBold, result, u.TextReset)
 }