leetcode 15

public enum Q15 {
    instance;

    // 官网解法
    public List<List<Integer>> threeSum(int[] nums) {
        int n = nums.length;
        Arrays.sort(nums);
        List<List<Integer>> ans = new ArrayList<List<Integer>>();
        // 枚举 a
        for (int first = 0; first < n; ++first) {
            // 需要和上一次枚举的数不相同
            if (first > 0 && nums[first] == nums[first - 1]) {
                continue;
            }
            // c 对应的指针初始指向数组的最右端
            int third = n - 1;
            int target = -nums[first];
            // 枚举 b
            for (int second = first + 1; second < n; ++second) {
                // 需要和上一次枚举的数不相同
                if (second > first + 1 && nums[second] == nums[second - 1]) {
                    continue;
                }
                // 需要保证 b 的指针在 c 的指针的左侧
                while (second < third && nums[second] + nums[third] > target) {
                    --third;
                }
                // 如果指针重合，随着 b 后续的增加
                // 就不会有满足 a+b+c=0 并且 b<c 的 c 了，可以退出循环
                if (second == third) {
                    break;
                }
                if (nums[second] + nums[third] == target) {
                    List<Integer> list = new ArrayList<Integer>();
                    list.add(nums[first]);
                    list.add(nums[second]);
                    list.add(nums[third]);
                    ans.add(list);
                }
            }
        }
        return ans;
    }

    // 
    public List<List<Integer>> threeSum1(int[] nums) {
        List<List<Integer>> lists=new ArrayList<>();
        if(nums==null||nums.length<3)return lists;
        int l=nums.length;
        QuickSort.sort(nums);
        for(int i=0;i<l;i++){
            if(nums[i]>0){break;}
            for(int j=i+1;j<l;j++){
                for(int k=j+1;k<l;k++){
                    // -1 -1 3 4 没必要
                    if(-(nums[i]+nums[j])<nums[k]){
                        break;
                    }
                    if(!isRepetitive(lists,nums[i],nums[j],nums[k])&&
                            nums[i]+nums[j]+nums[k]==0){
                        lists.add(buildList(nums[i],nums[j],nums[k]));
                    }

                }
            }
        }

        return lists;
    }

    private List<Integer> buildList(int... num){
        List<Integer> list=new ArrayList<>();
        if(num==null||num.length==0)return list;
        for(int i:num){
            list.add(i);
        }
        return list;
    }

    private boolean isRepetitive(List<List<Integer>> lists,int i,int j,int k){
        return lists.stream().anyMatch(list-> {
            boolean b = list.stream().allMatch(e -> e == i);
            // 0特殊处理
            boolean c = ((i != j || i != k || i != 0) || b) &&
             (list.contains(i) && list.contains(j) && list.contains(k));
            return b||c;
        });
    }


    public static void main(String[] args) {
        System.out.println(Q15.instance.threeSum(new int[]{-1, 0, 1, 2, -1, -4}));
        System.out.println(Q15.instance.threeSum1(new int[]{-1, 0, 1, 2, -1, -4}));
        System.out.println(Q15.instance.threeSum1(new int[]{0,0,0}));
        System.out.println(Q15.instance.threeSum1(new int[]{-4,-2,1,-5,-4,-4,4,-2,0,4,0,-2,3,1,-5,0,0}));
        System.out.println(Q15.instance.threeSum(new int[]{-4,-2,1,-5,-4,-4,4,-2,0,4,0,-2,3,1,-5,0,0}));
    }

}