added index_to_cubecoord and cubecoord_to_index

src/main/java/com/codingame/game/CubeCoord.java

@@ -2,6 +2,8 @@
 
 import com.codingame.view.Serializer;
 
+import java.lang.Math;
+
 public class CubeCoord {
     static int[][] directions = new int[][] { { 1, -1, 0 }, { +1, 0, -1 }, { 0, +1, -1 }, { -1, +1, 0 }, { -1, 0, +1 }, { 0, -1, +1 } };
     int x, y, z;
@@ -77,4 +79,58 @@ public CubeCoord getOpposite() {
         CubeCoord oppositeCoord = new CubeCoord(-this.x, -this.y, -this.z);
         return oppositeCoord;
     }
+
+    public static CubeCoord index_to_cubecoord(int index){
+        // index to Cube coordinates (pointy) conversion.
+        if (index==0) return new CubeCoord(0, 0, 0);
+
+        int i = 1 + (int) Math.floor((Math.sqrt(12 * index - 3) - 3.0) / 6.0);
+        int l_min = 1 + 3 * (i - 1) * i; // min index in this circle
+        // int l_max = 3 * i * (i + 1);  // max index in this circle
+        int x1 = index - l_min;          // linear offset 
+
+        // euclidian div : x1 = a * i + d
+        int o = x1 / i; // orientation index
+        int d = x1 % i; // direction index
+
+        int xi = directions[o][0] * i + directions[(o+2) % 6][0] * d;
+        int yi = directions[o][1] * i + directions[(o+2) % 6][1] * d;
+        int zi = directions[o][2] * i + directions[(o+2) % 6][2] * d;
+
+        return new CubeCoord(xi, yi, zi);
+    }
+
+
+    public static int cubecoord_to_index(int x, int y, int z){
+        // index to Cube coordinates (pointy) conversion.
+        if (x==0 && y==0 && z==0) return 0;
+
+        int I = Math.max(Math.abs(x), Math.max(Math.abs(y), Math.abs(z)));
+        int i_off = 1 + 3 * (I - 1) * I;
+
+        int index;
+        if (x == I)
+            index = i_off + 0 * I - z;
+        else if (z == -I)
+            index = i_off + 1 * I + y;
+        else if (y == I)
+            index = i_off + 2 * I - x;
+        else if (x == -I)
+            index = i_off + 3 * I + z;
+        else if (z == I)
+            index = i_off + 4 * I - y;
+        else // if (y == -I)
+            index = i_off + 5 * I + x;
+
+        return index;
+    }
+
+    public static int cubecoord_to_index(CubeCoord cubecoord){
+        return cubecoord_to_index(cubecoord.x, cubecoord.y, cubecoord.z);
+    }
+
+    public int cubecoord_to_index(){
+        return cubecoord_to_index(this.x, this.y, this.z);
+    }
+
 }