1089 The longest palindrome substring V2 (Manacher algorithm)

1089 Longest Palindromic Substring V2 (Manacher's Algorithm)

Base Time Limit: 1 second Space Limit: 131072 KB Score: 0  Difficulty: Basic

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Palindromic strings refer to left-right symmetrical strings such as aba, abba, cccbccc, and aaaa.

Input a string Str, output the length of the longest palindromic substring in Str.

Input

Enter Str (Length of Str <= 100000)

Output

Output the length L of the longest palindrome substring.

Input example

print

Output example

5

Idea: Manacher (horse carriage algorithm) https://blog.csdn.net/sunny_hun/article/details/79977680

#include<iostream>
#include<cstring>
using namespace std;

char str[100100];
char s[200200];

intmain()
{
	cin>>str;
    int i,j,maxx=1;
    int n=strlen(str);
    for(i=n;i>=1;i--)
    {
        s[i*2+1]='#';
        s[i*2]=str[i-1];
    }
    s[0]='$';
    s[1]='#';
    n=strlen(s);
    s[n]='\0';
    int mx;//The rightmost position of the largest palindrome substring
    int id;//The center position of the largest palindrome substring
    int p[200200]; //The radius of the largest palindrome substring centered on i
    for(int i=1;i<n;i++)
    {
        if(i<mx)
            p[i]=min(p[2*id-i],mx-i); //The radius of i is left/right of mx, p[j],mx-i
        else
            p[i]=1;
        while(s[i-p[i]]==s[i+p[i]])
            p[i]++;
        if(i+p[i]>mx) //The center of the largest palindrome substring becomes i
        {
            id=i;
            mx=i+p[i];
        }
        maxx=max(maxx,p[i]-1);
    }
    cout<<maxx<<endl;
	return 0;
}