Add Solution.java for 0448.Find All Numbers Disappeared in an Array

Author: huaxu1024

solution/0448.Find All Numbers Disappeared in an Array/README_EN.md

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+# Find All Numbers Disappeared in an Array
+
+Given an array of integers where **1 ≤ a[i] ≤ n** (n = _size of array_), some elements appear twice and others appear once.
+
+Find all the elements of [1, _n_] inclusive that do not appear in this array.
+
+Could you do it without extra space and in O(_n_) runtime? You may assume the returned list does not count as extra space.
+
+## Example:
+```
+ Input: [4,3,2,7,8,2,3,1]
+ Output: [5,6]
+```

solution/0448.Find All Numbers Disappeared in an Array/Solution.java

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+class Solution {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        List<Integer> result = new ArrayList<>();
+        boolean[] inx = new boolean[nums.length + 1];
+        for (int num : nums) {
+            inx[num] = true;
+        }
+        for (int i = 1, length = nums.length; i <= length; i++) {
+            if (!inx[i]) {
+                result.add(i);
+            }
+        }
+        return result;
+    }
+}

solution/0448.Find All Numbers Disappeared in an Array/Solution2.java

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+class Solution {
+    public List<Integer> findDisappearedNumbers(int[] nums) {
+        List<Integer> result = new ArrayList<>();
+        for (int i = 0, length = nums.length; i < length; i++) {
+            int abs = Math.abs(nums[i]);
+            nums[abs - 1] = -Math.abs(nums[abs - 1]);
+        }
+        for (int i = 0, length = nums.length; i < length; i++) {
+            if (nums[i] > 0) {
+                result.add(i+1);
+            }
+        }
+        return result;
+    }
+}