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diff --git a/‎ActivityZero/src/ActivityZero.java‎
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+import java.util.ArrayList;
+import java.util.List;
+import java.util.Scanner;
+
+/**
+ * User: ning wei
+ * Date: 5/2/12
+ * Time: 8:23 PM
+ *
+ * You'll be given a list of activities and their caloric impact.
+ * Write a program that outputs the names of activities a Dropboxer should choose to partake in
+ * so that the sum of their caloric impact is zero.
+ * Once an activity is selected, it cannot be chosen again.
+ *
+ * It is a question to find a sum to zero from all possible elements of an array
+ * Basically use gray code to pick element from a given array and calculate the sum
+ *
+ */
+
+public class ActivityZero {
+    private String activity;
+    private int calorie;
+
+    public ActivityZero(String a, int c) {
+        this.activity = a;
+        this.calorie = c;
+    }
+
+    public static void main(String args[]) {
+
+        List<ActivityZero> listActivityZero = new ArrayList<ActivityZero>();
+
+        Scanner scanner = new Scanner(System.in);
+
+        //TODO: input exception is not handled.
+
+        int n = Integer.parseInt(scanner.nextLine());
+        while (n > 0) {
+            String newInput = scanner.nextLine();
+            String[] tempArray = newInput.split(" ");
+
+            ActivityZero az = new ActivityZero(tempArray[0], Integer.parseInt(tempArray[1]));
+            listActivityZero.add(az);
+
+            n--;
+
+        }
+
+        scanner.close();
+
+        List<ActivityZero> tmpList = new ArrayList<ActivityZero>();
+        sumCalorie(listActivityZero, listActivityZero.size(), tmpList, true);
+
+    }
+
+    public static void sumCalorie(List<ActivityZero> list, int n, List<ActivityZero> tmpList, boolean pick) {
+        if (n == 0)
+            return; // start recursion back
+        sumCalorie(list, n - 1, tmpList, true);
+        if (pick) {
+            tmpList.add(list.get(n - 1));
+            showSum(tmpList);
+        } else {
+            tmpList.remove(list.get(n - 1));
+            showSum(tmpList);
+        }
+        sumCalorie(list, n - 1, tmpList, false);
+
+    }
+
+    public static void showSum(List<ActivityZero> l) {
+        int sumCalorie = 0;
+        for (ActivityZero az : l) {
+            sumCalorie += az.calorie;
+
+        }
+        if (l.size() != 0 && sumCalorie == 0) {
+            System.out.println("The winner picks: ");
+            for (ActivityZero az : l) {
+                System.out.println(az.activity + " " + az.calorie);
+            }
+        }
+    }
+
+
+}