hdu 3613 扩展kmp求回文串

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新建一个串为给定串的反转，
原串跟新串匹配求得是前缀回文，
新串跟原串匹配求得是后缀回文。

#include<cstdio>#include<cstring>#include<string>#include<algorithm>#include<iostream>#include<vector>using namespace std;int va[30],pre[510000],last[510000],nexta[510000],nextb[510000],l;string a,b;bool sumPre[510000],sumLast[510000];void getNext(string a,int *nexta,int la){       int i=0,j = -1;       nexta[0] = -1;       while(i<la)       {           if(a[i]==a[j]||j==-1)           {               i++,j++;               nexta[i] = j;           }           else j = nexta[j];       }}void kmp(string a,int la,string b,int *nexta,bool *sum){      int i=0,j=0;      while(j<l)      {          if(a[i]==b[j]||i==-1)          {              i++;j++;          }          else i = nexta[i];      }      int pre = i;      while(pre)      {        sum[pre] = true;        pre = nexta[pre];      }}int main(){    int t;    ios::sync_with_stdio(false);    scanf("%d",&t);    while(t--)    {        for(int i=0;i<26;i++) scanf("%d",&va[i]);        cin>>a;        l = a.size();        int sum = 0;        for(int i=0;i<=l;i++)        {            sumPre[i] = false;            sumLast[i] = false;        }        for(int i=0;i<l;i++)        {            sum+=va[a[i]-'a'];            pre[i] = sum;        }        sum = 0;        for(int i=l-1;i>=0;i--)        {            sum+=va[a[i]-'a'];            last[i] = sum;        }        b = a;        reverse(b.begin(),b.end());        getNext(a,nexta,l);        kmp(a,l,b,nexta,sumPre);        getNext(b,nextb,l);        kmp(b,l,a,nextb,sumLast);        int ans = -1000000000;        for(int i=0;i<l-1;i++)        {            sum = 0;            //printf("%d %d\n",sumPre[i+1],sumLast[l-i-1]);            if(sumPre[i+1])sum+=pre[i];            if(sumLast[l-i-1])sum+=last[i+1];            ans = max(ans,sum);        }        printf("%d\n",ans);    }    return 0;}

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