problem: four sum

Author: RootHex200

problem48/main.dart

@@ -0,0 +1,31 @@
+
+void main(List<String> args) {
+  print(fourSum([1,0,-1,0,-2,2],0));
+  print(fourSum([2,2,2,2,2], 8));
+}
+  List<List<int>> fourSum(List<int> nums, int target) {
+    nums.sort();
+    List<List<int>> result = [];
+    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 left = j + 1, right = nums.length - 1;
+        while (left < right) {
+          int sum = nums[i] + nums[j] + nums[left] + nums[right];
+          if (sum == target) {
+            result.add([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 < target) {
+            left++;
+          } else {
+            right--;
+          }
+        }
+      }
+    }
+    return result;
+  }