Solve the problem #442

Author: rayworks

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

@@ -0,0 +1,39 @@
+package org.sean.array;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.LinkedList;
+import java.util.List;
+
+/***
+ * 442. Find All Duplicates in an Array
+ */
+public class DuplicatesFinder {
+    public List<Integer> findDuplicates(int[] nums) {
+        if (nums == null || nums.length <= 1)
+            return Collections.emptyList();
+
+        int length = nums.length;
+
+        int mask = ~(1 << 31);
+        List<Integer> result = new LinkedList<>();
+
+        for (int i = 0; i < length; i++) {
+            int pos = (nums[i] & mask) - 1;
+
+            int flag = (nums[pos] >> 31) & 0x01;
+            if (flag == 1) { // already marked
+                result.add(nums[i] & mask);
+            } else {
+                nums[pos] = (1 << 31) | nums[pos];// mark the value
+            }
+        }
+        return result;
+    }
+
+    public static void main(String[] args) {
+        int[] array = {4, 3, 2, 7, 8, 2, 3, 1};
+        List<Integer> duplicates = new DuplicatesFinder().findDuplicates(array);
+        System.out.println(Arrays.toString(duplicates.toArray()));
+    }
+}