15 3Sum

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class No15 {

public static void main(String[] args) {
int[] nums = { -1, 0, 1, 2, -1, -4 };
System.out.println(threeSum(nums));
}

public static List<List<Integer>> threeSum(int[] nums) {

Arrays.sort(nums);
List<List<Integer>> result = new ArrayList<List<Integer>>();

for (int i = 0; i < nums.length; i++) {
int k = i + 1;
int l = nums.length - 1;

if (nums[i] > 0)   //原先没有这两句，超时，加上这两个if后就不超时了
break;
if (i > 0 && nums[i] == nums[i - 1])
continue;

while (k < l) {
int sum = nums[i] + nums[k] + nums[l];
if (sum < 0)
k++;
else if (sum > 0)
l--;
else {
List<Integer> list = new ArrayList<Integer>();
list.add(nums[i]);
list.add(nums[k]);
list.add(nums[l]);
if (!result.contains(list))
result.add(list);
k++;
l--;
}
}
}
return result;
}
}