leetcode new problems

leetcode/lc15/notes.md

@@ -0,0 +1,7 @@
+The intuition in this problem is we first sort the entire list and then fix i on first index and j at i+1 and k at last index and then compute total ,if(total>0) then since it is sorted, we need to bring total down so we do k-- and if total<0 then j++
+
+To avoid recomputations for same j, we do j++ until nums[j]!=nums[j-1]
+
+TC : o(nlogn) + o(n*n);  SC : o(1)
+
+

leetcode/lc15/threesome.cpp

@@ -0,0 +1,25 @@
+class Solution{
+    public:
+        vector<vector<int>> ThreeSum(vector<int> &nums){
+            vector<vector<int>> res;
+            sort(nums.begin(), nums.end());
+            int n = nums.size();
+            for(int i =0;i<n;i++){
+                if(nums[i]>0) break;
+                if(i>0 && nums[i]==nums[i-1]) continue;
+                int j = i+1;
+                int k = nums.size() -1;
+                while(j<k){
+                    int total = nums[i]+nums[j]+nums[k];
+                    if(total>0) k--;
+                    else if(total<0) j++;
+                    else{
+                        res.push_back({nums[i], nums[j], nums[k]});
+                        j++;
+                        while(j<k && nums[j] == nums[j-1]) j++;
+                    }
+                }
+            }
+            return res;
+        }
+};