15. 3Sum

import java.util.*;public class Solution {    public List<List<Integer>> threeSum(int[] nums) {        List<List<Integer>> res = new ArrayList<>();        Arrays.sort(nums);        Set<ThreeSum> threeSumSet = new TreeSet<ThreeSum>();        for(int i = 0; i < nums.length; ++i) {            for(int j = i + 1; j < nums.length; ++j) {                int sum = nums[i] + nums[j];                sum = -sum;                boolean is_have = find_sum(j+1, nums.length-1, nums, sum);                if(!is_have) continue;                int k[] = new int[] {nums[i], nums[j], sum};                Arrays.sort(k);                ThreeSum threeSum = new ThreeSum(k[0], k[1], k[2]);                threeSumSet.add(threeSum);            }        }        ThreeSum tmp = null;        for(Iterator<ThreeSum> iterator = threeSumSet.iterator(); iterator.hasNext(); ) {            ThreeSum threeSum = iterator.next();            if(tmp == null) res.add(Arrays.asList(new Integer[]{threeSum.a, threeSum.b, threeSum.c}));            else if(threeSum.a == tmp.a && threeSum.b == tmp.b && threeSum.c == tmp.c) continue;            else {                tmp = threeSum;                res.add(Arrays.asList(new Integer[]{threeSum.a, threeSum.b, threeSum.c}));            }        }        return res;    }    public boolean find_sum(int low, int high, int[] nums, int target) {        while (low <= high) {            int mid = (low + high) / 2;            if(nums[mid] == target) return true;            else if(nums[mid] > target) high = mid-1;            else if(nums[mid] < target) low = mid+1;        }        return false;    }    private class ThreeSum implements Comparable<ThreeSum>{        int a, b, c;        public ThreeSum(int a, int b, int c) {            this.a = a;            this.b = b;            this.c = c;        }        @Override        public int compareTo(ThreeSum o) {            if(a < o.a) return -1;            else if(a == o.a) {                if(b < o.b) return -1;                else if(b == o.b) {                    if(c<o.c) return -1;                    else if( c == o.c) return 0;                    else return 1;                } else return 1;            } else return 1;        }    }//    public static void main(String[] args) {//        Solution solution = new Solution();//        List<List<Integer>> res = solution.threeSum(new int[] {-4,-2,-2,-2,0,1,2,2,2,3,3,4,4,6,6});//        for(int i = 0; i < res.size(); ++i) {//            for(int j = 0; j < res.get(i).size(); ++j) {//                System.out.print(res.get(i).get(j) + " ");//            }//            System.out.println();//        }//    }}