15. 3Sum

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