4Sum.cpp

c++/4Sum.cpp

@@ -0,0 +1,46 @@
+class Solution {
+public:
+    vector<vector<int>> fourSum(vector<int>& nums, int target) {
+        int n = nums.size();
+        sort(nums.begin(), nums.end());
+        set<vector<int>> set;
+        vector<vector<int>> output;
+        for(int i=0; i<n-3; i++){
+            for(int j=i+1; j<n-2; j++){
+                long long newTarget = (long long)target - (long long)nums[i] - (long long)nums[j];
+                int low = j+1, high = n-1;
+                while(low < high){
+                    if(nums[low] + nums[high] < newTarget){
+                        low++;
+                    }
+                    else if(nums[low] + nums[high] > newTarget){
+                        high--;
+                    }
+                    else{
+                        set.insert({nums[i], nums[j], nums[low], nums[high]});
+                        low++; high--;
+                    }
+                }
+            }
+        }
+        for(auto it : set){
+            output.push_back(it);
+        }
+        return output;
+    }
+};
+
+
+
+
+
+
+/*
+
+    Time Complexity : O(N^3), Here Three nested loop creates the time complexity. Where N is the size of the
+    array(nums).
+
+    Space Complexity : O(1), Constant space. Extra space is only allocated for the Vector(output), however the
+    output does not count towards the space complexity.
+
+    Solved using Array(Three Nested Loop) + Sorting. Optimized Approach.