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原题：

/** * Created by gouthamvidyapradhan on 29/03/2017. * Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. * <p> * Note: The solution set must not contain duplicate triplets. * <p> * For example, given array S = [-1, 0, 1, 2, -1, -4], * <p> * A solution set is: * [ * [-1, 0, 1], * [-1, -1, 2] * ] */

答案：

public class ThreeSum {    /**     * Main method     *     * @param args     * @throws Exception     */    public static void main(String[] args) throws Exception {        int[] nums = {-1, 0, 1, 2, -1, -4, -1, 0, 1, 2, -1, -4, -1, 0, 1, 2, -1, -4, -1, 0, 1, 2, -1, -4, -1, 0, 1, 2, -1, -4, -1, 0, 1, 2, -1, -4, -1, 0, 1, 2, -1, -4, -1, 0, 1, 2, -1, -4};        System.out.println(new ThreeSum().threeSum(nums));    }    public List<List<Integer>> threeSum(int[] nums) {        List<List<Integer>> result = new ArrayList<>();        if (nums.length < 3) return result;        Arrays.sort(nums);        for (int i = 0, l = nums.length; i < l - 2; i++) {            if (i == 0 || nums[i] != nums[i - 1]) {                int j = i + 1, k = l - 1;                while (k > j) {                    if (j != i + 1 && nums[j] == nums[j - 1]) {                        j++;                        continue;                    }                    int sum = nums[i] + nums[j] + nums[k];                    if (sum == 0) {                        result.add(Arrays.asList(nums[i], nums[j], nums[k]));                        k--;                        j++;                    } else if (sum > 0) k--;                    else j++;                }            }        }        return result;    }}

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