Merge pull request neetcode-gh#1446 from VigneshIyer25/main

create: 448-Find-All-Numbers-Disappeared-In-An-Array

Author: Ahmad-A0

cpp/448-Find-All-Numbers-Disappeared-In-An-Array.cpp

@@ -0,0 +1,26 @@
+class Solution {
+public:
+    /*
+    Approach: 
+    Traverse the entire array from start to end. Since the numbers are in a range [1, n] we can use this simple trick.
+    At every index mark the position arr[arr[i]] as negative.
+    Repeat this for every index in the array.
+    At the end, which ever places are positive, add them to our answer.
+    
+    Time complexity: O(n)
+    Space complexity: O(1)
+    */
+    vector<int> findDisappearedNumbers(vector<int>& nums) {
+        vector<int> ans;
+        
+        for(int x : nums){                 /* Mark values as negative */
+            int currentVal = abs(x);
+            nums[currentVal-1] = 0 - abs(nums[currentVal-1]);
+        }
+        
+        for(int i = 1; i <= nums.size(); i++)
+            if(nums[i-1] > 0) ans.push_back(i);    /* Find unmarked values */
+        
+        return ans;
+    }
+};