3sum solution

Author: ohgyulim

3sum/ohgyulim.java

@@ -0,0 +1,34 @@
+import java.util.*;
+
+class Solution {
+    /* 시간 복잡도: O(N^2)
+    * - for 루프: O(N)
+    *   - while 루프: O(N) -> N^2
+    * 공간 복잡도: O(K), answer의 K = List<Integer> 개수
+    */ 
+    public List<List<Integer>> threeSum(int[] nums) {
+        Arrays.sort(nums);
+
+        List<List<Integer>> answer = new ArrayList<>();
+        for (int i = 0; i < nums.length - 2; i++) {
+            if (i > 0 && nums[i] == nums[i - 1]) continue;
+
+            int left = i + 1;
+            int right = nums.length - 1;
+
+            while (left < right) {
+                int sum = nums[i] + nums[left] + nums[right];
+                if (sum == 0) {
+                    answer.add(List.of(nums[i], nums[left], nums[right]));
+                    while (left < right && nums[left] == nums[left + 1]) left += 1;
+                    while (left < right && nums[right] == nums[right - 1]) right -= 1;
+                    left += 1;
+                    right -= 1;
+                } else if (sum < 0) left += 1;
+                else right -= 1;
+            }
+        }
+
+        return answer;
+    }
+}