UVAlive 7041 The Problem to Slow Down You（回文树）

题目链接：

https://icpcarchive.ecs.baylor.edu/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=5053

先把第一个串插入回文树中，然后把s数组清空插入第二个串，统计两个cnt数组，答案是二者相乘的结果

#include <iostream>
#include <stdlib.h>
#include <algorithm>
#include <stdio.h>
#include <math.h>
#include <string.h>

using namespace std;
typedef long long int LL;
const int maxn=2e5+5;
char str1[maxn];
char str2[maxn];
int n;
LL ans;
struct Tree
{
	const static int maxn=4e5+5;
    int next[maxn][26];
    int fail[maxn];
    LL  cnt[maxn];
    LL  cnt2[maxn];
    int len[maxn];
    int s[maxn];
    int last,p,n;
    int new_node(int x)
    {
        memset(next[p],0,sizeof(next[p]));
        cnt[p]=0;
        cnt2[p]=0;
        len[p]=x;
        return p++;
    }
       void init()
    {
        //memset(cnt,0,sizeof(cnt));
        //memset(cnt2,0,sizeof(cnt2));
        p=0;
        new_node(0);
        new_node(-1);
        last=0;
        n=0;
        s[0]=-1;
        fail[0]=1;
    }
    void init2()
    {
        last=0;
        s[0]=-1;
		fail[0]=1;
        n=0;
    }
    int get_fail(int x)
    {
        while(s[n-len[x]-1]!=s[n])
            x=fail[x];
        return x;
    }
    void add(int x)
    {
        x-='a';
        s[++n]=x;
        int cur=get_fail(last);
        if(!(last=next[cur][x]))
        {
            int now=new_node(len[cur]+2);
            fail[now]=next[get_fail(fail[cur])][x];
            next[cur][x]=now;
            last=now;
        }
        cnt[last]++;
    }
    void add2(int x)
    {
        x-='a';
        s[++n]=x;
        int cur=get_fail(last);
        if(!(last=next[cur][x]))
        {
            int now=new_node(len[cur]+2);
            fail[now]=next[get_fail(fail[cur])][x];
            next[cur][x]=now;
            last=now;
        }
        cnt2[last]++;
    }

    void count()
    {
        for(int i=p-1;i>=0;i--)
            cnt[fail[i]]+=cnt[i];
    }
    void count2()
    {
        for(int i=p-1;i>=0;i--)
            cnt2[fail[i]]+=cnt2[i];
    }
    void fun()
    {
        for(int i=2;i<=p-1;i++)
        {
            ans+=cnt[i]*cnt2[i];
        }
    }

}tree;
int main()
{
    scanf("%d",&n);
    for(int j=1;j<=n;j++)
    {
        scanf("%s%s",str1,str2);
        tree.init();
        int len=strlen(str1);
        int len1=strlen(str2);
        for(int i=0;i<len;i++)
        {
            tree.add(str1[i]);
        }
        tree.count();
        tree.init2();
        ans=0;
        for(int i=0;i<len1;i++)
        {
            tree.add2(str2[i]);
        }
        tree.count2();
        tree.fun();
        printf("Case #%d: %lld\n",j,ans);
    }
    return 0;
}