Create 4sum.java

4sum.java

@@ -0,0 +1,30 @@
+class Solution {
+    public List<List<Integer>> fourSum(int[] nums, int target) {
+        Arrays.sort(nums); 
+        List<List<Integer>> list = new ArrayList<>();
+        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;
+                twoSum(i, j, (long)target, nums, list);
+            }
+        }
+        return list;
+    }
+    public void twoSum(int i, int j, long target, int[] nums, List<List<Integer>> list){
+        long modifiedTarget = target - (nums[i] + nums[j]);
+        int left = j + 1, right = nums.length - 1;
+        while(left < right){
+            int sum = nums[left] + nums[right];
+            if(sum == modifiedTarget){
+                list.add(Arrays.asList(
+                    nums[i], nums[j], nums[left], nums[right]));
+                left++; right--;
+                while(left < right && nums[left] == nums[left - 1]) left++;
+                while(left < right && nums[right] == nums[right + 1]) right--;
+            }
+            else if(sum > modifiedTarget) right--;
+            else left++;
+        }
+    }
+}