diff --git a/include/s0018_4sum.hpp b/include/s0018_4sum.hpp
new file mode 100644
index 0000000..a446e24
--- /dev/null
+++ b/include/s0018_4sum.hpp
@@ -0,0 +1,14 @@
+#ifndef S0018_4SUM
+#define S0018_4SUM
+
+#include <vector>
+#include <algorithm>
+
+using namespace std;
+
+class Solution {
+ public:
+  vector<vector<int>> fourSum(vector<int>& nums, int target);
+};
+
+#endif
diff --git a/src/s0018_4sum.cpp b/src/s0018_4sum.cpp
new file mode 100644
index 0000000..f203504
--- /dev/null
+++ b/src/s0018_4sum.cpp
@@ -0,0 +1,28 @@
+#include "s0018_4sum.hpp"
+
+vector<vector<int>> Solution::fourSum(vector<int>& nums, int target) {
+  int len = nums.size();
+  if (len < 4) {
+    return {};
+  }
+  vector<vector<int>> result{};
+  sort(nums.begin(), nums.end());
+  for (int i{1}; i < len - 2; i++) {
+    for (int j = len - 2; j > i; j--) {
+      for (int x{0}, y = len - 1; x < i && y > j;) {
+        if (nums[x] + nums[y] + nums[i] + nums[j] > target) {
+          y--;
+        } else if (nums[x] + nums[y] + nums[i] + nums[j] < target) {
+          x++;
+        } else {
+          vector<int> v = {nums[x], nums[i], nums[j], nums[y]};
+          if (std::find(result.begin(), result.end(), v) == result.end()) {
+            result.push_back(v);
+          }
+          x++;
+        }
+      }
+    }
+  }
+  return result;
+}
diff --git a/tests/s0018_4sum.cpp b/tests/s0018_4sum.cpp
new file mode 100644
index 0000000..03269f4
--- /dev/null
+++ b/tests/s0018_4sum.cpp
@@ -0,0 +1,19 @@
+#include "s0018_4sum.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem18, Case1) {
+  vector<int> nums{1, 0, -1, 0, -2, 2};
+  int target{0};
+  vector<vector<int>> sum{{-2, -1, 1, 2}, {-2, 0, 0, 2}, {-1, 0, 0, 1}};
+  Solution solution;
+  EXPECT_EQ(solution.fourSum(nums, target), sum);
+}
+
+TEST(Problem18, Case2) {
+  vector<int> nums{2, 2, 2, 2, 2};
+  int target{8};
+  vector<vector<int>> sum{{2, 2, 2, 2}};
+  Solution solution;
+  EXPECT_EQ(solution.fourSum(nums, target), sum);
+}