[leetcode#49] Group anagrams

problem:

Given an array of strings, group anagrams together.

For example, given: ["eat", "tea", "tan", "ate", "nat", "bat"] ,
Return:

["  ate", "eat", "tea"],  ["Nat", "Tan"],  ["bat"]]

Note:

1. For the return value, each inner list ' s elements must follow the lexicographic order.
2. All inputs'll is in lower-case.

Wrong solution 1:

 Public classSolution { PublicList<list<string>>groupanagrams (string[] strs) {if(STRs = =NULL)            Throw NewIllegalArgumentException ("STRs is null"); List<List<String>> ret =NewArraylist<list<string>> (); if(Strs.length = = 0) {Ret.add (NewArraylist<string> ()); returnret; } Comparator<String> Comp =NewComparator<string>() {@Override Public intCompare (String str1, String str2) {returnStr1.compareto (STR2);        }        };        Arrays.sort (STRs, comp); HashMap<string, arraylist<string>> map =NewHashmap<string, arraylist<string>> ();  for(String str:strs) {string Sorted_str=sortstr (str); if(Map.containskey (sorted_str)) {Map.get (SORTED_STR). Add (str); } Else{ArrayList<String> item =NewArraylist<string> ();                Item.add (str);            Map.put (Sorted_str, item); }        }        returnret; }            Privatestring Sortstr (String str) {Char[] Char_array =Str.tochararray ();        Arrays.sort (Char_array); returnchar_array.tostring (); }}

MistakesAnalysis:

mistake:input:[""]output:[]expected:[[""]]analysis:1. Misunderstood "" withNULL. "is also accounted as a string, it just has no character. But the string "had a reference forit. [""] is a String array with only one element, the element is ""string. We must tackle it as a valid input. And there is a stupid the bug in above solution. Not because the ability to handle""string. the""would work a valid string to go through all the code. The problem forAbove solution is:i forget to add the newly created arraylist<string> into RET set!!! -----------------------------------------------------------ArrayList<String> item =NewArraylist<string>(); Item.add (str); Map.put (sorted_str, item); Fix:arraylist<String> item =NewArraylist<string>(); Item.add (str); Ret.add (item); Map.put (SORTED_STR, item) ;-----------------------------------------------------------2. There is also a block of extra code. The Arrays.sort () function acutally could handle the sort among strings, no need to implement any extra comparator. Sort (object[] a) sorts the specified array of objects into ascending order, according to the natural ordering of its elemen Ts.------------------------------------------------------------------------------http://docs.oracle.com/javase/7/docs/api/java/lang/comparable.htmlThe natural ordering means the CompareTo method defined in theclass.------------------------------------------------------------------------------compareTo (String anotherstring) compares, strings lexicographically.

Wrong Solution 2:

 Public classSolution { PublicList<list<string>>groupanagrams (string[] strs) {if(STRs = =NULL)            Throw NewIllegalArgumentException ("STRs is null"); List<List<String>> ret =NewArraylist<list<string>> (); if(Strs.length = = 0) {ArrayList temp=NewArraylist<string> (); returnret;        } arrays.sort (STRs); HashMap<string, arraylist<string>> map =NewHashmap<string, arraylist<string>> ();  for(String str:strs) {string Sorted_str=sortstr (str); if(Map.containskey (sorted_str)) {Map.get (SORTED_STR). Add (str); } Else{ArrayList<String> item =NewArraylist<string> ();                Item.add (str);                Ret.add (item);            Map.put (Sorted_str, item); }        }        returnret; }        Privatestring Sortstr (String str) {Char[] Char_array =Str.tochararray ();        Arrays.sort (Char_array); returnchar_array.tostring (); }}

MistakesAnalysis:

mistakes:input:["", ""]output:[[""],[""]]expected:[["", ""Char   Char[].tostring (), it returns the array ' s reference in String form, like: [[email protected]CH Arnew  String. return New String (Char_array);

Solution:

 Public classSolution { PublicList<list<string>>groupanagrams (string[] strs) {if(STRs = =NULL)            Throw NewIllegalArgumentException ("STRs is null"); List<List<String>> ret =NewArraylist<list<string>> (); if(Strs.length = = 0)             returnret;        Arrays.sort (STRs); HashMap<string, arraylist<string>> map =NewHashmap<string, arraylist<string>> ();  for(String str:strs) {string Sorted_str=sortstr (str); if(Map.containskey (sorted_str)) {Map.get (SORTED_STR). Add (str); } Else{ArrayList<String> item =NewArraylist<string> ();                Item.add (str);                Ret.add (item);            Map.put (Sorted_str, item); }        }        returnret; }        Privatestring Sortstr (String str) {Char[] Char_array =Str.tochararray ();        Arrays.sort (Char_array); return NewString (Char_array); }}

[leetcode#49] Group anagrams