add second approach in find duplicate solution (CodingWallah#15)

Author: rath23

ArraysSolutions/Find All Duplicates in an Array.md

@@ -1,5 +1,7 @@
 ## Solution of Find All Duplicates in an Array
 
+### First Approach 
+
 #### Time Complexity - O (n)
 
 #### Space Complexity - O(1)
@@ -39,7 +41,35 @@ return list;
 }
 
 ```
+### Second Approach
+
+#### Time Complexity - O (n)
+
+#### Space Complexity - O(1)
+
+```java
+class Solution {
+ public List<Integer> findDuplicates(int[] nums) {
+ List <Integer> list = new ArrayList <Integer>();
+ int n = nums.length;
+ int index; 
+ for (int i = 0 ; i < n; i++){
+ int num = nums[i];
+ index = Math.abs(num) - 1 ;
+ if ( nums[index] < 0){
+ list.add(Math.abs(nums[i]));
+ }
+ else{
+ nums[index] = nums[index] * -1;
+ }
+ }
+ return list;
+ }
+}
+
+```
+
 
 <div align="right"> 
  Contributed By <a href="https://github.com/rath23"> Muneer Ahmad</a>
-</div>
+</div>