k sum in leetcode

public class  {
	public int[] twoSum(int[] nums, int target) {
		int[] result = new int[2];
		Map<Integer, Integer> map = new HashMap<Integer, Integer>();
		for (int i = 0; i < nums.length; i++) {
			if (map.containsKey(target - nums[i])) {
				result[1] = i + 1;
				result[0] = map.get(target - nums[i]);
				return result;
			}
			map.put(nums[i], i + 1);
		}
		return result;
	}
}

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

public class  {
	public List<List<Integer>> fourSum(int[] nums, int target) {
		List<List<Integer>> result = new ArrayList<>();
		if(nums.length<4) return result;
		Arrays.sort(nums);
		for(int i = 0; i < nums.length-3; i++){
			if(i>0&&nums[i]==nums[i-1])continue;                      
			for(int j = i + 1; j< nums.length-2;j++){
				if(j>i+1&&nums[j]==nums[j-1])continue;
				int left = j+1;
				int right = nums.length-1;
				while(left<right){
					int sum = nums[i] + nums[j] + nums[left] + nums[right];
					if(sum==target){
						result.add(Arrays.asList(nums[i],nums[j],nums[left],nums[right]));
						while(left<right&&nums[left]==nums[left+1])left++;               
						while(left<right&&nums[right]==nums[right-1])right--;            
						left++;
						right--;
					}else if(sum<target) left++;
					else right--;
				}
			}
		}
		return result;
	}
}