15. 3Sum

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> ret=new ArrayList<List<Integer>>();
        Arrays.sort(nums);
        for(int i=0;i<nums.length-2;i++)
            if(i==0||nums[i]!=nums[i-1])
            {
                int l=i+1;
                int r=nums.length-1;
                while(l<r)
                {
                    int sum=nums[i]+nums[l]+nums[r];
                    if(sum==0)
                    {
                        ret.add(Arrays.asList(new Integer[]{nums[i], nums[l], nums[r]}));
                        while(l<r&&nums[l]==nums[l+1])l++;
                        while(l<r&&nums[r]==nums[r-1])r--;
                        l++;
                        r--;
                    }
                    else if(sum>0)
                        r--;
                    else
                        l++;
                }
            }
        return ret;
    }
}