diff --git a/Hard/10. Regular Expression Matching/soljava.java b/Hard/10. Regular Expression Matching/soljava.java
deleted file mode 100644
index 1bf35e4..0000000
--- a/Hard/10. Regular Expression Matching/soljava.java	
+++ /dev/null
@@ -1,32 +0,0 @@
-class Solution {
-
-
-    public boolean isMatch(String s, String p) {
-        int m = s.length(), n = p.length();
-        Boolean[][] M = new Boolean[m+1][n]; // Why Boolean: null indicates the sub-problem not processed yet
-        return dfs(s, p, 0, 0, m, n, M);  // The problem: to match s[i, m), p[j, n)
-    }
-
-
-    // the sub-problem: to match[i, m
-
-
-    private boolean dfs(String s, String p, int i, int j, int m, int n, Boolean[][] M) {
-        if (j == n) return i == m;
-        if (M[i][j] != null) return M[i][j];
-
-        char c2 = p.charAt(j);
-        if (j < n - 1 && p.charAt(j + 1) == '*')
-            return M[i][j] = dfs(s, p, i, j+2, m, n, M) || // do not match 'x*' , x means any char or . (use'*' as 0 char)
-                    i < m && match(s.charAt(i), c2) && dfs(s, p, i+1, j, m, n, M); // match 1 char in string for '*'
-
-        return M[i][j] = i < m && match(s.charAt(i), c2) && dfs(s, p, i+1, j+1, m, n, M); // match 1 char from both sides
-    }
-
-
-    private boolean match(char c1, char c2) {
-        if (c2 == '.') return true;
-        return c1 == c2;
-    }
-    
-}
\ No newline at end of file
diff --git a/Medium/18. 4Sum/Solution.java b/Medium/18. 4Sum/Solution.java
new file mode 100644
index 0000000..6dcc1e0
--- /dev/null
+++ b/Medium/18. 4Sum/Solution.java	
@@ -0,0 +1,50 @@
+public class Solution {
+        public List<List<Integer>> fourSum(int[] nums, int target) {
+            List<List<Integer>> ans = new ArrayList<>();
+            Arrays.sort(nums);
+            
+            for (int i = 0; i < nums.length - 3; i++) {
+                if (i > 0 && nums[i] == nums[i - 1]) {
+                    continue;
+                }
+                
+                for (int j = i + 1; j < nums.length - 2; j++) {
+                    if (j > i + 1 && nums[j] == nums[j - 1]) {
+                    continue;
+                }
+                
+                int k = j + 1;
+                int l = nums.length - 1;
+                
+                while (k < l) {
+                     long sum = (long) nums[i] + nums[j] + nums[k] + nums[l];
+                        
+                    if (sum == target) {
+                        List<Integer> temp = new ArrayList<>();
+                        temp.add(nums[i]);
+                        temp.add(nums[j]);
+                        temp.add(nums[k]);
+                        temp.add(nums[l]);
+                        ans.add(temp);
+                            
+                        k++;
+                        l--;
+                            
+                        while (k < l && nums[k] == nums[k - 1]) {
+                            k++;
+                        }
+                        
+                        while (k < l && nums[l] == nums[l + 1]) {
+                            l--;
+                        }
+                    } else if (sum < target) {
+                        k++;
+                    } else {
+                        l--;
+                    }
+                }
+            }
+        }
+        return ans;
+    }
+}