[Leetcode]15 3Sum

https://oj.leetcode.com/problems/3sum/

Public class solution {    public list<list<integer>>  threesum (Int[] num)  {                 // solution a        // return  threesum_sort (num);                 // solution b        return threesum_map ( NUM);    }        ////////////////////     // solution a: sort    //    // o (n^2)     private list<list<integer>> threesum_sort (Int[] numbers)     {        Set<List<Integer>>  Toreturn = new HashSet<> ();                 // sort        arrays.sort (Numbers);                 int len =  numbers.length;        for  (int i = 0 ;  i < len ; i ++)         {             // Fix i.             // move index j from i -> len             // index k from len  to i;            int j =  i + 1;            int k = len - 1;             while  (j < k)              {                 int sum = numbers[i] + numbers[ j] + numbers[k];                 if  (sum == 0)                  {                     List<Integer> r = new ArrayList<> ();                      r.add (numberS[i]);                     r.add (Numbers[j]);                     r.add (Numbers[k]);                     toreturn.add (R);                     j  ++;                     k --;                 }                 else if  (sum > 0)                  {                     k --;                 }                 else                  {                     j ++;                 }            }         }        return new arraylist <List<Integer>> (Toreturn);    }                 // Solution A: Map    //     // o (n^2)     private List<List<Integer>>  Threesum_map (Int[] num)     {        Set< List<integer>> toreturn = new hashset<> ();                 map<integer, integer> map  = new HashMap<> (        int len =);  num.length;        for  (int i = 0 ;  i < len ; i ++)         {             map.put (num[i], i);         }                for  (int i  = 0 ; i < len ; i ++)          {            for  (int j  = i + 1 ; j < len ; j ++)              {                 int sum = num[i] + num[j];                                  integer pos = map.get (-sum);                 if  (POS  != null) &NBSP;&AMP;&Amp;  (POS&NBSP;!=&NBSP;I&NBSP;&AMP;&AMP;&NBSP;POS&NBSP;!=&NBSP;J))  // a result found.                 {                      List<integer> r = new arraylist<integer> ();                     r.add (Num[i]);                      r.add (Num[j]);                     r.add (-sum);                     collections.sort (R);                      toreturn.add (R);                 }             }        }         return new ArrayList<List<Integer>> (Toreturn);     }        ////////////////////    // solution  a: brute force    //        //  Assume num.length >= 3    private List<List<Integer> > threesum_bruteforce (Int[] num)     {         Set<List<Integer>> toReturn = new HashSet<> ();         int len = num.length;        for  (int  i = 0 ; i < len ; i ++)          {            for  (int  j = i + 1 ; j < len ; j ++)              {                 for  (int k = j + 1 ; k <  len ; k ++)                  {                     if  (num[i] + num[j] + num[k] == 0)                      {                          List<Integer> r = new ArrayList<Integer> (Arrays.aslist (num[i ],&NBSP;NUM[J],&NBSP;NUM[K]);                         collections.sort (R);                          toreturn.add (R);                     }                 }            }         }        return new arraylist<list< Integer>> (Toreturn);     }}

[Leetcode]15 3Sum