URAL 1297 SA

URAL 1297

题意 求回文串 跟求在两个串里面的最长公共子串求法一样 但是要特判 n-maxx!=height[i]+minn 的时候需要continue掉 因为对着的位置不同 就不能回文

/*
    if you can't see the repay
    Why not just work step by step
    rubbish is relaxed
    to ljq
*/
#include <cstdio>
#include <cstring>
#include <iostream>
#include <queue>
#include <cmath>
#include <map>
#include <stack>
#include <set>
#include <sstream>
#include <vector>
#include <stdlib.h>
#include <algorithm>
using namespace std;

#define dbg(x) cout<<#x<<" = "<< (x)<< endl
#define dbg2(x1,x2) cout<<#x1<<" = "<<x1<<" "<<#x2<<" = "<<x2<<endl
#define dbg3(x1,x2,x3) cout<<#x1<<" = "<<x1<<" "<<#x2<<" = "<<x2<<" "<<#x3<<" = "<<x3<<endl
#define max3(a,b,c) max(a,max(b,c))
#define min3(a,b,c) min(a,min(b,c))

typedef pair<int,int> pll;
typedef long long ll;
const int inf = 0x3f3f3f3f;
const int _inf = 0xc0c0c0c0;
const ll INF = 0x3f3f3f3f3f3f3f3f;
const ll _INF = 0xc0c0c0c0c0c0c0c0;
const ll mod =  (int)1e9+7;

ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}
ll ksm(ll a,ll b,ll mod){int ans=1;while(b){if(b&1) ans=(ans*a)%mod;a=(a*a)%mod;b>>=1;}return ans;}
ll inv2(ll a,ll mod){return ksm(a,mod-2,mod);}
const int MAX_N = 2e3+5;
int wa[MAX_N],wb[MAX_N],wsf[MAX_N],wv[MAX_N],sa[MAX_N];
int Rank[MAX_N],height[MAX_N],s[MAX_N];
char str1[MAX_N],str2[MAX_N];
int cmp(int *r,int a,int b,int k)
{
    return r[a]==r[b]&&r[a+k]==r[b+k];
}
void getsa(int *r,int *sa,int n,int m)//n为添加0后的总长
{
    int i,j,p,*x=wa,*y=wb,*t;
    for(i=0; i<m; i++)  wsf[i]=0;
    for(i=0; i<=n; i++)  wsf[x[i]=r[i]]++;
    for(i=1; i<m; i++)  wsf[i]+=wsf[i-1];
    for(i=n; i>=0; i--)  sa[--wsf[x[i]]]=i;
    p=1;
    j=1;
    for(; p<=n; j*=2,m=p)
    {
        for(p=0,i=n+1-j; i<=n; i++)  y[p++]=i;
        for(i=0; i<=n; i++)  if(sa[i]>=j)  y[p++]=sa[i]-j;
        for(i=0; i<=n; i++)  wv[i]=x[y[i]];
        for(i=0; i<m; i++)  wsf[i]=0;
        for(i=0; i<=n; i++)  wsf[wv[i]]++;
        for(i=1; i<m; i++)  wsf[i]+=wsf[i-1];
        for(i=n; i>=0; i--)  sa[--wsf[wv[i]]]=y[i];
        t=x;
        x=y;
        y=t;
        x[sa[0]]=0;
        for(p=1,i=1; i<=n; i++)
            x[sa[i]]=cmp(y,sa[i-1],sa[i],j)? p-1:p++;
    }
}

void getheight(int *r,int n)//n为添加0后的总长
{
    int i,j,k=0;
    for(i=1; i<=n; i++)  Rank[sa[i]]=i;
    for(i=0; i<n; i++)
    {
        if(k)
            k--;
        else
            k=0;
        j=sa[Rank[i]-1];
        while(r[i+k]==r[j+k])
            k++;
        height[Rank[i]]=k;
    }
}
int main()
{
    //ios::sync_with_stdio(false);
    //freopen("a.txt","r",stdin);
    //freopen("b.txt","w",stdout);
    scanf("%s",str1);
    int len = strlen(str1),n=0,ans = 1,xb=0;
    for(int i = 0;i<len;++i)
        str2[i] = str1[len-i-1];
    for(int i = 0;i<len;++i)
        s[n++] = str1[i]-'A'+1;
    s[n++] = 60;
    for(int i = 0;i<len;++i)
        s[n++] = str2[i]-'A'+1;
    s[n] = 0;
    getsa(s,sa,n,70);
    getheight(s,n);
    for(int i = 2;i<=n;++i)
    {
        int maxx = max(sa[i],sa[i-1]);
        int minn = min(sa[i],sa[i-1]);
        if(maxx<len||minn>len) continue;
        if(n-maxx != height[i]+minn) continue;
                if(height[i]>ans)
                {
                    xb  = min(sa[i],sa[i-1]);
                    ans = height[i];
                }
                else if(height[i]==ans)
                {
                xb = min(xb,min(sa[i],sa[i-1]));
                }

    }
    for(int i = xb;ans--;++i)
        printf("%c",s[i]-1+'A');
    printf("\n");
    //fclose(stdin);
    //fclose(stdout);
    //cout << "time: " << (long long)clock() * 1000 / CLOCKS_PER_SEC << " ms" << endl;
    return 0;
}