3Sum_OCT11.java

//haha
class Solution{
    public List<List<Integer>> threeSum(int[] nums){
        List<List<Integer>> results = new ArrayList<>();
        if(nums.length < 3) return results;
        Arrays.sort(nums);
        //i j k are indexs
        int i = 0;
        while(i < nums.length - 2){
            if(nums[i]>0) break;
            int j = i + 1;
            int k = nums.length - 1;
            while(j<k){
                int sum = nums[i] + nums[j] + nums[k];
                if(sum == 0) results.add(Arrays.asList(nums[i],nums[j],nums[k]));
                //try diff j and k with given i
                if(sum <= 0) while(nums[j] == nums[++j] && j < k);//deal duplicates
                if(sum >= 0) while(nums[k] == nums[--k] && j < k);//deal duplicates
            }
            while(nums[i] == nums[++i] && i < nums.length -2);//deal duplicates
        }
        return results;
    }
}