Leetcode algorithm Collation

The largest palindrome in a string (question 5th)

Given A string s, find the longest palindromic substring in S. Assume that the maximum length of SIS 1000.

Example:

Input: "Babad" Output: "Bab" note: "ABA" is also a valid answer.

Example:

Input: "CBBD" Output: "BB"

1. My solution (accepted): Center expansion

Idea: Palindrome means that there is a center, a traversal, for each position on the number of the largest palindrome can be, the initial processing pruning, merging the same elements, such as xxxxaaaxxxx, the first constant level of a merge out; Traverse time to prune again, traversed by a maxlen, if the element is about to traverse the maximum possible palindrome length can not exceed maxlen, no longer traverse.

1      Public Static voidMain (string[] args) {2String str = "Ababababa";3 System.out.println (Longestpalindrome (str));4 5     }6 7      Public Staticstring Longestpalindrome (string s) {8         if(s = =NULL) {9             return NULL;Ten         } One         Char[] chars =S.tochararray (); A         intLength =chars.length; -         intMaxLen = 0; -String maxstr = ""; the  -          for(inti = 0; i < length; i++) { -  -             //Cut Branch +             intPossiblelength =getmaxpossiblelength (i, length); -             if(Possiblelength <maxlen) { +                 Continue; A             } at  -String maxstrtmp =Getmaxstrbyindex (i, chars); -             if(MaxLen <maxstrtmp.length ()) { -MaxLen =maxstrtmp.length (); -Maxstr =maxstrtmp; -             } in         } -         returnMaxstr; to     } +  -     Private Static intGetmaxpossiblelength (intIndexintlength) { the         intHead = 0; *         intTail = length-1; $         if(index = = Head | | index = =tail) {Panax Notoginseng             return1; -         } the         intRESULT1 = index-head; +         intRESULT2 = Tail-index; A  the         intmin = result1 <= result2?result1:result2; +         returnMin * 2 + 1; -     } $  $     Private StaticString Getmaxstrbyindex (intIndexChar[] chars) { -StringBuilder SB =NewStringBuilder (string.valueof (Chars[index)); -         intLength =chars.length; the         intHead = Index-1; -         intTail = index + 1;Wuyi  the         //Middle Deal -          while(true) { Wu             if(Head >= 0 && chars[index] = =Chars[head]) { -Sb.insert (0, string.valueof (chars[head--])); About}Else if(Tail <= length-1 && chars[index] = =Chars[tail]) { $Sb.append (String.valueof (chars[tail++])); -}Else { -                  Break; -             } A         } +  the         //besides deal -          while(true) { $             if(Head < 0 | | tail > LENGTH-1) { the                  Break; the             } the             if(Head >= 0 && tail <= length-1 && chars[head] = =Chars[tail]) { theSb.insert (0, string.valueof (chars[head--])); -Sb.append (String.valueof (chars[tail++])); in                 Continue; the             } the              Break; About  the         } the         returnsb.tostring (); the}

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2. DP Solution

Leetcode algorithm Collation