Merge pull request #860 from KillMonger1/4sumcpp

18 | 4Sum | Medium CPP

C++/4Sum.cpp

@@ -0,0 +1,42 @@
+// https://leetcode.com/problems/4sum/
+class Solution {
+public:
+    vector<vector<int>> fourSum(vector<int>& nums, int target) {
+        sort(nums.begin(),nums.end());
+        int i=0;
+        vector<vector<int>> res;
+        while(i<nums.size()){
+            int a1=nums[i];
+            int j=i+1;
+            while(j<nums.size()){
+                int a2=nums[j];
+                int tgt=target-a1-a2;
+                int front=j+1;
+                int back=nums.size()-1;
+                while(front<back){
+                    int sm=nums[front]+nums[back];
+                    if(sm>tgt){
+                        back--;
+                    }else if(sm<tgt){
+                        front++;
+                    }else{
+                        int f=nums[front];
+                        int b=nums[back];
+                        res.push_back({a1,a2,f,b});
+                        while(front<back && nums[front]==f)
+                            front++;
+                        while(front<back && nums[back]==b)
+                            back--;
+                    }
+                }
+                while(j+1<nums.size()&&nums[j]==nums[j+1])
+                    j++;
+                j++;
+            }
+            while(i+1<nums.size()&&nums[i]==nums[i+1])
+                i++;
+            i++;
+        }
+        return res;
+    }
+};