@@ -41,8 +41,12 @@ public int ladderLength(String beginWord, String endWord, List<String> wordList)
4141Set <String >startSet =new HashSet <>();
4242Set <String >endSet =new HashSet <>();
4343Set <String >visited =new HashSet <>();
44+
4445startSet .add (beginWord );
45- if (dict .contains (endWord ))endSet .add (endWord );// all transformed words must be in dict (including endWord)
46+ if (dict .contains (endWord )) {
47+ endSet .add (endWord );// all transformed words must be in dict (including endWord)
48+ }
49+
4650for (int len =2 ; !startSet .isEmpty ();len ++) {
4751Set <String >nq =new HashSet <>();
4852for (String w :startSet ) {
@@ -52,11 +56,16 @@ public int ladderLength(String beginWord, String endWord, List<String> wordList)
5256if (c ==w .charAt (j ))continue ;// beginWord and endWord should not be the same
5357ch [j ] =c ;
5458String nb =String .valueOf (ch );
55- if (endSet .contains (nb ))return len ;// meet from two ends
56- if (dict .contains (nb ) &&visited .add (nb ))nq .add (nb );// not meet yet, visited is safe to use
59+ if (endSet .contains (nb )) {
60+ return len ;// meet from two ends
61+ }
62+ if (dict .contains (nb ) &&visited .add (nb )) {
63+ nq .add (nb );// not meet yet, visited is safe to use
64+ }
5765 }
5866 }
5967 }
68+
6069startSet = (nq .size () <endSet .size ()) ?nq :endSet ;// switch to small one to traverse from other end
6170endSet = (startSet ==nq ) ?endSet :nq ;
6271 }