Create Day6.java

Author: nsiwnf

Day6.java

@@ -0,0 +1,49 @@
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Day6 {
+
+  public static int part1(int[] blocks) {
+    List<Integer> iterations = redistributeBlocks(blocks.clone());
+    return iterations.size() - 1;
+  }
+
+  public static int part2(int[] blocks) {
+    List<Integer> iterations = redistributeBlocks(blocks.clone());
+    int repeat = iterations.remove(iterations.size() - 1);
+    return iterations.size() - iterations.indexOf(repeat);
+  }
+
+  private static List<Integer> redistributeBlocks(int[] blocks) {
+    List<Integer> iterations = new ArrayList<>();
+    int hashCode = Arrays.hashCode(blocks);
+    while (!iterations.contains(hashCode)) {
+
+      // find max
+      int max = -1;
+      int idx = 0;
+      for (int i = 0; i < blocks.length; i++) {
+        if (blocks[i] > max) {
+          max = blocks[i];
+          idx = i;
+        }
+      }
+
+      // redistribute
+      blocks[idx] = 0;
+      while (max-- > 0) {
+        idx = (idx + 1) % blocks.length;
+        blocks[idx]++;
+      }
+
+      // log iteration
+      iterations.add(hashCode);
+      hashCode = Arrays.hashCode(blocks);
+    }
+
+    iterations.add(hashCode);
+    return iterations;
+  }
+
+}