Longest palindrome---hdu3068 (palindrome string manacher algorithm template)

Title Link: http://acm.hdu.edu.cn/showproblem.php?pid=3068

Test instructions is clear: it is to find the length of the longest palindrome in a string s substring; This type of problem uses the Manacher algorithm

Manacher algorithm (copy of the Great God's explanation):

Definition array P[i] denotes I-centric (including I, the character) the length of the palindrome string

The string s is previously swept to the back for (int i=0;i<strlen (s); ++i) to calculate p[i], then the largest p[i] is the longest palindrome string length, then the question is how to seek p[i]?

Since S is previously swept back, it must have been calculated when P[i] is needed p[1]....p[i-1]

Suppose you now scan to the location of I+k and now need to calculate p[i+k]

Defines maxlen as the right-most place to reach in all palindrome strings before the i+k position, that is, Maxlen=p[i]+i;//p[i]+i represents the largest

In two cases:

1.i+k This position is not in the front of any palindrome string, that is, I+k>maxlen, then the initialization p[i+k]=1;//itself is a palindrome string

Then P[i+k] extends around, i.e. while (s[i+k+p[i+k]] = = S[i+k-p[i+k]) ++p[i+k]

2.i+k This position is contained by a palindrome string in front of position I, i.e. maxlen>i+k

In this case P[i+k] is not starting from 1

Because of the nature of palindrome string, we know i+k this position about I and i-k symmetry,

So P[i+k] is divided into the following 3 situations to draw

Black is the palindrome range of I, Blue is the range of I-k palindrome string,

#include <stdio.h>#include<string.h>#include<algorithm>#include<stdlib.h>using namespacestd;Const intN = 1e6+7;CharS[n];intP[n];intManacher (CharS[],intN) {    intIndex =0, MaxLen =0;  for(intI=2; i<n; i++)    {        if(MaxLen >i) p[i]= Min (p[index*2-I.], maxlen-i); ElseP[i]=1;  while(s[i-p[i]]==s[i+P[i]]) P[i]++; if(i+p[i]>maxlen) {MaxLen= i+P[i]; Index=i; }    }    intAns =0;  for(intI=2; i<n; i++) ans=Max (ans, p[i]); returnans-1;}intMain () { while(SCANF ("%s", s)! =EOF) {memset (P,0,sizeof(p)); intLen =strlen (s);  for(intI=len; i>=0; i--) {s[i+i+2] =S[i]; S[i+i+1] ='#'; } s[0] ='$'; intAns = manacher (S,2*len+2); printf ("%d\n", ans); }    return 0;}

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Longest palindrome---hdu3068 (palindrome string manacher algorithm template)