Add a solution for Leetcode#448.

Author: rayworks

src/main/java/org/sean/array/ElementFinder.java

@@ -0,0 +1,39 @@
+package org.sean.array;
+
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+
+/**
+ * Created by Sean on 2/24/17.
+ * <p>
+ * 448. Find All Numbers Disappeared in an Array
+ */
+public class ElementFinder {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        if (nums.length <= 1)
+            return Collections.EMPTY_LIST;
+
+        LinkedList<Integer> result = new LinkedList<Integer>();
+        int cnt = nums.length;
+
+        // used to clear the most left bit if assigned before
+        int mask = ~(1 << 31);
+
+        // 4, 3, 2, 7, 8, 2, 3, 1
+        for (int i = 0; i < cnt; i++) {
+            int pos = (nums[i] & mask) - 1;
+            nums[pos] = (1 << 31) | nums[pos];// mark the value
+        }
+
+        for (int k = 1; k <= cnt; k++) {
+            int v = nums[k - 1];
+            byte s = (byte) (v >> 31);
+            if ((s & 0x01) == 0) {
+                result.add(k);
+            }
+        }
+
+        return result;
+    }
+}

src/test/java/ElementFinderTest.java

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+import org.junit.Assert;
+import org.junit.Test;
+import org.sean.array.ElementFinder;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Created by Sean on 2/24/17.
+ */
+public class ElementFinderTest {
+    @Test
+    public void testMissingNums() {
+        ElementFinder finder = new ElementFinder();
+
+        int[] all = {4, 3, 2, 7, 8, 2, 3, 1};
+        List<Integer> result = finder.findDisappearedNumbers(all);
+
+        Integer[] array = result.toArray(new Integer[result.size()]);
+        System.out.printf(Arrays.toString(array));
+        Assert.assertArrayEquals(new Integer[]{5, 6}, array);
+    }
+}