Added task 15.

src/main/java/s0015.three.sum/Solution.java

@@ -0,0 +1,44 @@
+package s0015.three.sum;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        Arrays.sort(nums);
+        final int len = nums.length;
+        List<List<Integer>> result = new ArrayList<>();
+        int l = 0, r = 0;
+        for (int i = 0; i < len - 2; i++) {
+            l = i + 1;
+            r = len - 1;
+            while (r > l) {
+                int sum = nums[i] + nums[l] + nums[r];
+                if (sum < 0) {
+                    l++;
+                } else if (sum > 0) {
+                    r--;
+                } else {
+                    List<Integer> list = new ArrayList<>();
+                    list.add(nums[i]);
+                    list.add(nums[l]);
+                    list.add(nums[r]);
+                    result.add(list);
+                    while (l < r && nums[l + 1] == nums[l]) {
+                        l++;
+                    }
+                    while (r > l && nums[r - 1] == nums[r]) {
+                        r--;
+                    }
+                    l++;
+                    r--;
+                }
+            }
+            while (i < len - 1 && nums[i + 1] == nums[i]) {
+                i++;
+            }
+        }
+        return result;
+    }
+}

src/test/java/s0015.three.sum/SolutionTest.java

@@ -0,0 +1,15 @@
+package s0015.three.sum;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.Test;
+
+public class SolutionTest {
+    @Test
+    public void threeSum() {
+        assertThat(
+                new Solution().threeSum(new int[] {-1, 0, 1, 2, -1, -4}).toString(),
+                equalTo("[[-1, -1, 2], [-1, 0, 1]]"));
+    }
+}