feb 2015 problem 9 and 10

uil/aplus-february-2015/9/Play.java

@@ -0,0 +1,41 @@
+import static java.lang.System.out;
+import java.util.Scanner;
+import java.io.File;
+import java.io.IOException;
+
+class Main {
+  public static void main(String[] args) throws IOException {
+    Scanner s = new Scanner(new File("play.dat"));
+    while(s.hasNextInt()) {
+        int magnitude = s.nextInt();
+        out.println(play(magnitude));
+        if(s.hasNextInt())
+            out.println();
+    }
+  }
+
+  // 3 =>     1 3 5 3 1       (5)
+  // 4 =>   1 3 5 7 5 3 1     (7)
+  // 5 => 1 3 5 7 9 7 5 3 1   (9)
+  // https://www.desmos.com/calculator/0gszz81jpx
+  // m = 2x - 1 (top)
+  // y = m - 2 * abs(x - ((m + 1) / 2))
+  public static String play(int mag) {
+      int[] counts = new int[(mag * 2) - 1];
+      String[] sequence = new String[counts.length];
+
+    for(int i = 1; i <= counts.length; i++)
+        counts[i - 1] = counts.length - (2 * Math.abs(i - (counts.length + 1) / 2));
+    for(int i = 0; i < counts.length; i++)
+        sequence[i] = repeat("*", counts[i]);
+    
+    return String.join("\n", sequence);
+  }
+
+  public static String repeat(String sub, int n) {
+    String result = "";
+    for(int i = 0; i < n; i++)
+        result += sub;
+    return result;
+  }
+}