Copy list with random pointers

C++/2Sum.cpp

@@ -0,0 +1,17 @@
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target)
+     {
+        unordered_map<int,int> mp;
+        for(int i=0;i<nums.size();i++)
+        {
+            if(mp.find(target -nums[i]) != mp.end())
+            {
+                return {mp[target- nums[i]],i};
+            }
+            else
+            mp[nums[i]]=i;
+        }
+         return  {};
+    }
+};

C++/4Sum.cpp

@@ -0,0 +1,36 @@
+class Solution {
+public:
+    vector<vector<int>> fourSum(vector<int>& nums, int target) 
+    {
+        vector<vector<int>> res;
+        if(nums.size() < 4) return res;
+        set<vector<int>> hash;
+        sort(nums.begin(), nums.end());
+        for(int i = 0; i < nums.size() - 2; i++) {
+            for(int j = i + 1; j < nums.size() - 1; j++)
+             {
+                int left = j + 1;
+                int right = nums.size() - 1;
+                while(left < right) 
+                {
+                    int sum = nums[i] + nums[left] + nums[right] + nums[j];
+                    if(sum == target && !hash.count({nums[i], nums[j], nums[left], nums[right]})) {
+                        hash.insert({nums[i], nums[j], nums[left], nums[right]});
+                        res.push_back({nums[i], nums[j], nums[left], nums[right]});
+                        left++;
+                        right--;
+                        while(left < right && nums[left] == nums[left - 1])
+                            left++;
+                        while(left < right && nums[right] == nums[right + 1])
+                            right--;
+                    }
+                    else if(target > sum) 
+                        left++;
+                    else
+                        right--;
+                }
+            }
+        }
+        return res;
+    }
+};

C++/Copy_Linkedlist_with_Random_Pointers.cpp

@@ -0,0 +1,36 @@
+class Node {
+public:
+    int val;
+    Node* next;
+    Node* random;
+
+    Node(int _val) {
+        val = _val;
+        next = NULL;
+        random = NULL;
+    }
+};
+class Solution {
+public:
+    Node* copyRandomList(Node* head)
+     {
+        unordered_map<Node*,Node*> mp;
+        Node* copy = nullptr;
+        Node* original = head;
+        while(original != NULL)
+        {
+            copy = new Node(original->val);
+            mp[original] = copy;
+            original= original->next;
+        }
+        original = head;
+        while(original != NULL)
+        {
+            copy = mp[original];
+            copy->next = mp[original->next];
+            copy->random = mp[original->random];
+            original = original->next;  
+        }
+        return mp[head];
+    }
+};