Update 3Sum - Leetcode 15.cpp

Author: gahogg

3Sum - Leetcode 15/3Sum - Leetcode 15.cpp

@@ -1,3 +1,5 @@
+
+// Hashmap Solution:
 #include <vector>
 #include <unordered_map>
 #include <set>
@@ -33,3 +35,46 @@ class Solution {
         return vector<vector<int>>(result.begin(), result.end());
     }
 };
+
+
+// Two Pointer Solution:
+#include <vector>
+#include <algorithm>
+
+using namespace std;
+
+class Solution {
+public:
+    vector<vector<int>> threeSum(vector<int>& nums) {
+        sort(nums.begin(), nums.end());
+        int n = nums.size();
+        vector<vector<int>> answer;
+
+        for (int i = 0; i < n; i++) {
+            if (nums[i] > 0) {
+                break;
+            }
+            if (i > 0 && nums[i] == nums[i - 1]) {
+                continue;
+            }
+            int lo = i + 1, hi = n - 1;
+            while (lo < hi) {
+                int sum = nums[i] + nums[lo] + nums[hi];
+                if (sum == 0) {
+                    answer.push_back({nums[i], nums[lo], nums[hi]});
+                    lo++;
+                    hi--;
+                    while (lo < hi && nums[lo] == nums[lo - 1]) lo++;
+                    while (lo < hi && nums[hi] == nums[hi + 1]) hi--;
+                } else if (sum < 0) {
+                    lo++;
+                } else {
+                    hi--;
+                }
+            }
+        }
+
+        return answer;
+    }
+};
+