三数之和-双指针-去重

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