problem Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
Note:
The solution set must not contain duplicate triplets.
Example:
1 2 3 4 5 6 7 Given array nums = [-1, 0, 1, 2, -1, -4], A solution set is: [ [-1, 0, 1], [-1, -1, 2] ]
approach 1 算法 暴力解法，3 层循环
复杂度
approach 2 算法 2 层+set
复杂度
approach 3 算法 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 class Solution public static List<List<Integer>> threeSum(int [] nums) { if (nums == null || nums.length < 3 ) { return Collections.EMPTY_LIST; } Set<List<Integer>> res = new HashSet<>(); Arrays.sort(nums); for (int i = 0 ; i < nums.length - 2 ; i++) { if (i >= 1 && nums[i] == nums[i - 1 ]) { continue ; } Set<Integer> set = new HashSet<>(); for (int j = i + 1 ; j < nums.length; j++) { if (set.contains(nums[j])) { res.add(Arrays.asList(nums[i], (-nums[i] - nums[j]), nums[j])); set.remove(nums[j]); } else { set.add(-nums[i] - nums[j]); } } } return new ArrayList<>(res); } }
复杂度
summery