hdu 4763 Theme Section 扩展kmp

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扩展kmp,next表求前缀和后缀的公共部分同时记录这个前缀是否在这个总串去除它长度的前缀和后缀后依然存在，最后拿出符合结果的最大前缀

#include<cstdio>#include<algorithm>#include<iostream>#include<cstring>using namespace std;char a[1000010];int nexta[1000010],la;bool sym[1000010];int getNext(){    int i=0,j=-1;    nexta[0] = -1;    while(i<la)    {        if(a[i]==a[j]||j==-1)        {            i++,j++;            nexta[i] = j;            if(i-1-j>=j-1&&i-1<=la-1-j)sym[j] = true;        }        else j = nexta[j];    }    int pre = nexta[la],ans = 0;    while(pre)    {        if(sym[pre])        {            ans = pre;            break;        }        else pre = nexta[pre];    }    return ans;}int main(){    int t;    scanf("%d",&t);    while(t--)    {        scanf("%s",a);        la = strlen(a);        for(int i=0;i<=la;i++)sym[i]=0;        printf("%d\n",getNext());    }    return 0;}

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