diff --git a/15_3_sum.cpp b/15_3_sum.cpp
new file mode 100644
index 0000000..1346886
--- /dev/null
+++ b/15_3_sum.cpp
@@ -0,0 +1,68 @@
+#include "test.h"
+
+
+class Solution {
+public:
+	vector<vector<int>> threeSum(vector<int>& nums)
+	{
+		vector<vector<int>> ret;
+
+		if (nums.size() < 3)
+			return ret;
+
+		sort(nums.begin(), nums.end());
+
+		for (auto i = 0u; i < nums.size() - 2; )
+		{
+			if (nums[i] > 0)
+				break;
+
+			auto j = i + 1;
+			auto k = nums.size() - 1; 
+			while (j < k)
+			{
+				auto sum = nums[i] + nums[j] + nums[k];
+
+				if (sum == 0)
+				{
+					ret.push_back({nums[i], nums[j++], nums[k--]});
+
+					//in the current while loop, i is constant, so make sure the next nums[j] is not equal to the current one
+					while (nums[j] == nums[j - 1] && j < k)
+						++j; 
+
+					//the same operation for k with the same reason
+					while (nums[k] == nums[k + 1] && j < k)
+						--k;
+				}
+				else
+					sum < 0 ? ++j : --k;
+			}
+
+			//make sure the next nums[i] is not equal to the current one
+			++i;
+			while (nums[i - 1] == nums[i] && i < j )
+				++i;
+		}
+		return ret;
+	}
+};
+
+
+
+int main()
+{
+	vector<vector<int>> datas = 
+	{
+		{-1, 0, 1, 2, -1, -4},
+		{0, 0 , 0},
+		{0, 0 , 0, 0},
+		{-2,0,1,1,2},
+		{-4,-2,-2,-2,0,1,2,2,2,3,3,4,4,6,6},
+		{},
+	};
+	Solution s;
+	for (auto& data : datas)
+		cout << s.threeSum(data) << endl;
+	return 0;
+}
diff --git a/Makefile b/Makefile
index ce51a5b..b43a8f6 100644
--- a/Makefile
+++ b/Makefile
@@ -13,6 +13,7 @@ targets = \
 	12_integer_to_roman.exec\
 	13_roman_to_integer.exec\
 	14_longest_common_prefix.exec\
+	15_3_sum.exec\
 
 
 CC = g++
diff --git a/test.h b/test.h
index d2f7cfd..89ea89f 100644
--- a/test.h
+++ b/test.h
@@ -37,7 +37,14 @@ using std::string;
 
 using std::vector;
 using std::map;
+using std::multimap;
 using std::unordered_map;
+using std::unordered_multimap;
+
+using std::set;
+using std::multiset;
+using std::unordered_set;
+using std::unordered_multiset;
 
 using namespace std::placeholders;