Improved task 18

Author: javadev

src/main/java/g0001_0100/s0018_4sum/Solution.java

@@ -1,6 +1,6 @@
 package g0001_0100.s0018_4sum;
 
-// #Medium #Array #Sorting #Two_Pointers #2022_10_07_Time_6_ms_(96.23%)_Space_44.3_MB_(76.54%)
+// #Medium #Array #Sorting #Two_Pointers #2023_03_15_Time_3_ms_(99.47%)_Space_43.2_MB_(35.71%)
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -9,55 +9,57 @@
 @SuppressWarnings("java:S135")
 public class Solution {
     public List<List<Integer>> fourSum(int[] nums, int target) {
-        List<List<Integer>> ret = new ArrayList<>();
-        if (nums.length < 4) {
-            return ret;
-        }
-        if (nums[0] == 1000000000 && nums[1] == 1000000000) {
-            return ret;
-        }
+        int n = nums.length;
         Arrays.sort(nums);
-        for (int i = 0; i < nums.length - 3; i++) {
-            if (i != 0 && nums[i] == nums[i - 1]) {
+        List<List<Integer>> result = new ArrayList<>();
+        for (int i = 0; i < n - 3; i++) {
+            if (i > 0 && nums[i] == nums[i - 1]) {
+                continue;
+            }
+            if ((long) nums[i] + nums[i + 1] + nums[i + 2] + nums[i + 3] > target) {
+                break;
+            }
+            if ((long) nums[i] + nums[n - 3] + nums[n - 2] + nums[n - 1] < target) {
                 continue;
             }
-            for (int j = i + 1; j < nums.length - 2; j++) {
-                if (j != i + 1 && nums[j] == nums[j - 1]) {
+            for (int j = i + 1; j < n - 2; j++) {
+                if (j > i + 1 && nums[j] == nums[j - 1]) {
                     continue;
                 }
-                int left = j + 1;
-                int right = nums.length - 1;
-                int half = nums[i] + nums[j];
-                if (half + nums[left] + nums[left + 1] > target) {
-                    continue;
+                if ((long) nums[j] + nums[j + 1] + nums[j + 2] > target - nums[i]) {
+                    break;
                 }
-                if (half + nums[right] + nums[right - 1] < target) {
+                if ((long) nums[j] + nums[n - 2] + nums[n - 1] < target - nums[i]) {
                     continue;
                 }
-                while (left < right) {
-                    int sum = nums[left] + nums[right] + half;
-                    if (sum == target) {
-                        ret.add(Arrays.asList(nums[left++], nums[right--], nums[i], nums[j]));
-                        while (nums[left] == nums[left - 1] && left < right) {
-                            left++;
+                int tempTarget = target - (nums[i] + nums[j]);
+                int low = j + 1;
+                int high = n - 1;
+                while (low < high) {
+                    int curSum = nums[low] + nums[high];
+                    if (curSum == tempTarget) {
+                        List<Integer> tempList = new ArrayList<>();
+                        tempList.add(nums[i]);
+                        tempList.add(nums[j]);
+                        tempList.add(nums[low]);
+                        tempList.add(nums[high]);
+                        result.add(tempList);
+                        low++;
+                        high--;
+                        while (low < high && nums[low] == nums[low - 1]) {
+                            low++;
                         }
-                        while (nums[right] == nums[right + 1] && left < right) {
-                            right--;
-                        }
-                    } else if (sum < target) {
-                        left++;
-                        while (nums[left] == nums[left - 1] && left < right) {
-                            left++;
+                        while (low < high && nums[high] == nums[high + 1]) {
+                            high--;
                         }
+                    } else if (curSum < tempTarget) {
+                        low++;
                     } else {
-                        right--;
-                        while (nums[right] == nums[right + 1] && left < right) {
-                            right--;
-                        }
+                        high--;
                     }
                 }
             }
         }
-        return ret;
+        return result;
     }
 }

src/test/java/g0001_0100/s0018_4sum/SolutionTest.java

@@ -14,7 +14,7 @@ void fourSum() {
                 new Solution().fourSum(new int[] {1, 0, -1, 0, -2, 2}, 0),
                 equalTo(
                         ArrayUtils.getLists(
-                                new int[][] {{1, 2, -2, -1}, {0, 2, -2, 0}, {0, 1, -1, 0}})));
+                                new int[][] {{-2, -1, 1, 2}, {-2, 0, 0, 2}, {-1, 0, 0, 1}})));
     }
 
     @Test