URAL 1297（后缀数组/Manacher算法）

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <queue>
//#include <tr1/unordered_set>
//#include <tr1/unordered_map>
#include <bitset>
//#pragma comment(linker, "/STACK:1024000000,1024000000")

using namespace std;

#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define inf 1e9
#define debug(a) cout << #a" = " << (a) << endl;
#define debugarry(a, n) for (int i = 0; i < (n); i++) { cout << #a"[" << i << "] = " << (a)[i] << endl; }
#define clr(x, y) memset(x, y, sizeof x)
#define ll long long
#define ull unsigned long long
#define FOR(i,a,b) \
for(i=a;a<b?i<=b:i>=b;a<b?i++:i--)

const int maxn =  1000*3+100;

char ma[maxn];
int mp[maxn],l;

void manacher(char *s,int len){
l=0;
ma[l++]='$';
ma[l++]='#';
for(int i=0;i<len;i++)
{
ma[l++]=s[i];
ma[l++]='#';
}
ma[l]=0;
int mx=0,id=0;
for(int i=0;i<l;i++)
{
mp[i]=mx>i?min(mp[2*id-i],mx-i):1;
while(ma[i+mp[i]]==ma[i-mp[i]]) mp[i]++;
if(i+mp[i]>mx)
{
mx=i+mp[i];
id=i;
}
}
}

char s[maxn];

int main()
{
//freopen("input.txt","r",stdin);
while(~scanf("%s",s))
{
int len=strlen(s);
manacher(s,len);
//printf("%s\n",ma);
int ans=-1 , pos=inf;
for(int i=0;i<l;i++)
{
if( mp[i] - 1 > ans  )
{
ans = mp[i]-1;
pos = i/2-mp[i]/2;
//printf("i %d mp[i] %d\n",i,mp[i]);
}
}
for(int i=0;i<ans;i++)
printf("%c",s[i+pos]);
printf("\n");
}
return 0;
}

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <queue>
//#include <tr1/unordered_set>
//#include <tr1/unordered_map>
#include <bitset>
//#pragma comment(linker, "/STACK:1024000000,1024000000")

using namespace std;

#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define inf 1e9
#define debug(a) cout << #a" = " << (a) << endl;
#define debugarry(a, n) for (int i = 0; i < (n); i++) { cout << #a"[" << i << "] = " << (a)[i] << endl; }
#define clr(x, y) memset(x, y, sizeof x)
#define ll long long
#define ull unsigned long long
#define FOR(i,a,b) \
for(i=a;a<b?i<=b:i>=b;a<b?i++:i--)

const int maxn =  1000*5+100;

struct suffix_array{
char s[maxn];
int sa[maxn],t[maxn],t2[maxn],c[maxn];
int n;
void build_sa(int m)
{
int i,*x=t,*y=t2;
FOR(i,0,m-1) c[i]=0;
FOR(i,0,n-1) c[x[i]=s[i]]++;
FOR(i,1,m-1) c[i]+=c[i-1];
FOR(i,n-1,0) sa[--c[x[i]]]=i;
for(int k=1;k<=n;k<<=1){
int p=0;
FOR(i,n-k,n-1) y[p++]=i;
FOR(i,0,n-1) if(sa[i]>=k) y[p++]=sa[i]-k;

FOR(i,0,m-1) c[i]=0;
FOR(i,0,n-1) c[x[y[i]]]++;

FOR(i,0,m-1) c[i]+=c[i-1];
FOR(i,n-1,0) sa[--c[x[y[i]]]]=y[i];

swap(x,y);
p=1;
x[sa[0]]=0;
FOR(i,1,n-1)
x[sa[i]]=y[sa[i-1]]==y[sa[i]]&&
y[sa[i-1]+k]==y[sa[i]+k]?p-1:p++;
if(p>=n) break;
m=p;
}
}
int Rank[maxn],height[maxn];
void getHeight(){
int k=0;
for(int i=0;i<n;i++) Rank[sa[i]]=i;
for(int i=0;i<n;i++)
{
if(k)k--;
int j=sa[Rank[i]-1];
while(s[i+k]==s[j+k]) k++;
height[Rank[i]]=k;
}
}
int d[maxn][20],flog[maxn];
void RMQ_init()
{
for(int i=0;i<n;i++) d[i][0]=height[i];
flog[0]=-1;
for(int i=1;i<n;i++) flog[i]=flog[i>>1]+1;
for(int j=1;(1<<j)<=n;j++)
for(int i=0;i+(1<<j)<=n;i++)
d[i][j] = min(d[i][j-1],d[i+(1<<(j-1))][j-1]);
}
int RMQ(int L,int R)
{
int k=flog[R-L+1];
return min(d[L][k],d[R-(1<<k)+1][k]);
}
int lcp(int j,int k)
{
if(j==k) return n-k;
if(Rank[j]>Rank[k]) swap(j,k);
return RMQ(Rank[j]+1,Rank[k]);
}
}su;

char s[maxn];

int main()
{
//freopen("input.txt","r",stdin);
while(~scanf("%s",s))
{
int len=strlen(s);
s[len]='$';
for(int i=0;i<len;i++)
s[2*len-i] = s[i];
s[2*len+1]=0;
//printf("%s\n",s);
su.n=2*len+2;
strcpy(su.s,s);
su.build_sa(255);
su.getHeight();
su.RMQ_init();
int ans=-1,pos=inf;
for(int i=0;i<len;i++)
{
int t = su.lcp(i,2*len-i);
int l = 2*t-1 , ip = i-t+1;
//printf("t %d i %d ip %d l %d\n",t,i,ip,l);
if( l == ans ) pos=min(pos,ip);
else if( l > ans )
{
ans=l;
pos=ip;
}
if( i )
{
int t = su.lcp(i,2*len-i+1);
int l = 2*t,ip = i-t;
if( l == ans ) pos=min(pos,ip);
else if( l > ans )
{
ans=l;
pos=ip;
//printf("t %d i %d ip %d l %d\n",t,i,ip,l);
}
}
}
for(int i=0;i<ans;i++)
printf("%c",s[i+pos]);
printf("\n");
}
return 0;
}