import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class ThreeSum {
public static List> threeSum(int[] nums) {
List
> res = new ArrayList<>();
if (nums == null || nums.length < 3) {
return res;
}
Arrays.sort(nums);
final int len = nums.length;
for (int i = 0; i <= len - 3; i++) {
if (i > 0 && nums[i] == nums[i - 1]) {
continue;
}
int start = i + 1, end = len - 1;
while (start < end) {
int sum = nums[i] + nums[start] + nums[end];
if (sum < 0) {
start++;
} else if (sum > 0) {
end--;
} else {
res.add(Arrays.asList(nums[i], nums[start++], nums[end--]));
while (start < end && nums[start] == nums[start - 1]) {
start++;
}
while (start < end && nums[end] == nums[end + 1]) {
end--;
}
}
}
}
return res;
}
}