"Leetcode" Palindrome Pairs (336)

1. Description

Given a list of unique words. Find all pairs of distinct indices (i, j) in the given list, so, the concatenation of the-words, i.e. is a palindrome.

　　Example 1:
Given words =["bat", "tab", "cat"]
Return[[0, 1], [1, 0]]
The palindromes is["battab", "tabbat"]

　　Example 2:
Given words =["abcd", "dcba", "lls", "s", "sssll"]
Return[[0, 1], [1, 0], [3, 2], [2, 4]]
The palindromes is["dcbaabcd", "abcddcba", "slls", "llssssll"]

2. Answer

 Public classSolution { PublicList<list<integer>>palindromepairs (string[] words) {List<List<Integer>> res =NewArraylist<list<integer>>(); if(Words = =NULL|| Words.length = = 0){          returnRes; }        //Build the Map Save the Key-val pairs:string-idxhashmap<string, integer> map =NewHashmap<>();  for(inti = 0; i < words.length; i++) {map.put (words[i], i); }        //Special Cases: "" can be combine with any palindrome string        if(Map.containskey ("")) {            intBlankidx = Map.get ("");  for(inti = 0; i < words.length; i++) {                if(Ispalindrome (Words[i])) {if(i = =blankidx)Continue;                    Res.add (Arrays.aslist (Blankidx, i));                Res.add (Arrays.aslist (i, blankidx)); }            }        }        //Find all string and reverse string pairs         for(inti = 0; i < words.length; i++) {String Cur_r=reversestr (Words[i]); if(Map.containskey (Cur_r)) {intFound =Map.get (Cur_r); if(found = = i)Continue;           Res.add (Arrays.aslist (i, found)); }        }        //find the pair s1, S2 that//Case1:s1[0:cut] is palindrome and s1[cut+1:] = reverse (s2) = (s2, s1)//case2:s1[cut+1:] is palindrome and s1[0:cut] = reverse (s2) = = (S1, s2)         for(inti = 0; i < words.length; i++) {String cur=Words[i];  for(intCut = 1; Cut < Cur.length (); cut++) {                if(Ispalindrome (cur.substring (0, cut))) {String Cut_r=Reversestr (cur.substring (cut)); if(Map.containskey (Cut_r)) {intFound =Map.get (Cut_r); if(found = = i)Continue;                    Res.add (arrays.aslist (found, i)); }                }                if(Ispalindrome (cur.substring (cut))) {String Cut_r= Reversestr (cur.substring (0, cut)); if(Map.containskey (Cut_r)) {intFound =Map.get (Cut_r); if(found = = i)Continue;                    Res.add (Arrays.aslist (i, found)); }                }            }        }           returnRes; }     Publicstring Reversestr (String str) {StringBuilder SB=NewStringBuilder (str); returnsb.reverse (). toString (); }     Public BooleanIspalindrome (String s) {inti = 0; intj = s.length ()-1;  while(I <=j) {            if(S.charat (i)! =S.charat (j)) {                return false; } I++; J--; }     return true; } }

"Leetcode" Palindrome Pairs (336)