Ural 1354. Palindrome. Again Palindrome KMP的应用

1354. Palindrome. Again Palindrome

Time limit: 1.0 second

Memory limit: 64 MB

A word is the nonempty sequence of symbols a1a2…an.
A palindrome is the word a1a2…an that
is read from the left to the right and from the right to the left the same way (a1a2…an = anan−1…a1).
IfS1 = a1a2…an and S2 = b1b2…bm,
then S1S2 = a1a2…anb1b2…bm.
The input contains some word S1. You are to find a nonempty word S2 of the minimal
length that S1S2 is a palindrome.

Input

The first input line contains S1 (it may consist only of the Latin letters). It’s guaranteed that the length of S1 doesn’t
exceed 10000 symbols.

Output

S1S2.

Samples

input	output
No	NoN
OnLine	OnLineniLnO
AbabaAab	AbabaAababA

Problem Author: Denis Nazarov

Problem Source: USU Junior Championship March'2005
构造回文串

#include <cstdio>
#include <cstdlib>
#include <cstring>
int i,j,l,next[10010];
char s[10010];
int main()
{
    scanf("%s",&s[1]);
    printf("%s",&s[1]);
    l=strlen(s+1);
    next[l]=l+1;
    i=l;
    j=l+1;
    while (i > 1)
        if ((j > l) || (s[i] == s[j]))
        {
            --i;
            --j;
            if (s[i] == s[j])
                next[i]=next[j];
            else  next[i]=j;
        }
        else  j=next[j];
    i=2;
    j=l;
    while (i <= l)
        if ((j > l) || (s[i] == s[j]))
            ++i,--j;
        else  j=next[j];
    for (; j!=0; --j)
        printf("%c",s[j]);
    printf("\n");
    return 0;
}