solution(java): 18. 4Sum

18. 4Sum
- Java

Author: godkingjay

Hard/10. Regular Expression Matching/soljava.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;
+    }
+}