[Leetcode] Remove Duplicate Letters

Topic:

"Bcabc""abc""CBACDCBC""acdb"

Analysis: By observing the rule of each letter subscript, taking "CBACDCBC" as an example,

The first step is to calculate the subscript (Countindex):

A  = 2,  b  = 1, 6c  = 0, 3, 5, 7D  and 4

The second step is to find the letter that meets the criteria (Findletter):

If the first subscript of a letter is less than the last subscript for each letter thereafter , the letter meets the criteria. For example, a of 2 is less than B of the 6,c of 7,d 4, then a 2 meet the conditions.

In the third step, remove the preceding subscript (Removeindex):

To set the letter x that matches the condition in the second step, delete all subscripts before the x subscript and delete x. For example, if X is a,x subscript 2, remove 0 from 1,c in B and remove a.

Repeat step two, step three until the collection is empty.

Take "CBACDCBC" as an example:

b  = 6c  = 3, 5, 7D  and 4

b  = 6d  = 4

The above transformation interpretation: Although 6 < 7, but 6 but > 4, so B does not meet, and C in 3 is less than the subsequent 4, so C in accordance with.

b  = 6

Finally, a-C,-B, acdb

The code is as follows:

     Publicstring Removeduplicateletters (string s) {StringBuilder res=NewStringBuilder (); HashMap<character, arraylist<integer>> HM =NewHashmap<character, arraylist<integer>>(); ArrayList<Character> reference =NewArraylist<character>();        Countindex (S, HM, reference);        Collections.sort (reference);  while(!Reference.isempty ()) {            intLettindex =Findletter (S, res, HM, reference);        Removeindex (Lettindex, HM, reference); }        returnres.tostring (); }        Private voidCountindex (String s, Hashmap<character, arraylist<integer>> hm, arraylist<character>reference) {         for(inti = 0; I < s.length (); i++) {            CharCH =S.charat (i); if(!hm.containskey (CH)) {ArrayList<Integer> tmp =NewArraylist<integer>();                Tmp.add (i);                Hm.put (CH, tmp);            Reference.add (CH); } Else{hm.get (ch). Add (i); }        }    }        Private intFindletter (String S, StringBuilder res, hashmap<character, arraylist<integer>> hm, Arraylist<character >reference) {        intm = 0;  for(inti = 0; I < reference.size (); i++) {m= Hm.get (Reference.get (i)). Get (0); intj = i+1;  for(; J < Reference.size (); j + +) {ArrayList<Integer> tmp =Hm.get (Reference.get (j)); if(M > Tmp.get (Tmp.size ()-1)) {                     Break; }            }            if(J = =reference.size ())                {Res.append (Reference.get (i));                Reference.remove (i);  Break; }        }        returnm; }        Private voidRemoveindex (intLett, Hashmap<character, arraylist<integer>> hm, arraylist<character>reference) {         for(inti = 0; I < reference.size (); i++) {ArrayList<Integer> tmp =Hm.get (Reference.get (i));  while(!tmp.isempty () && tmp.get (0) <Lett) {Tmp.remove (0); }        }    }

[Leetcode] Remove Duplicate Letters