hdu 5785 Interesting(manacher+前缀和)

 1 #include<bits/stdc++.h>
 2 #define F(i,a,b) for(int i=a;i<=b;++i)
 3 using namespace std;
 4 typedef long long ll;
 5 
 6 const int N=1e6+7,P=1e9+7;
 7 
 8 struct Manacher{
 9     char str[N*2];
10     int p[N*2],len,mx,id,tl,ans,i;
11     void maxlen(char *s){
12         len=strlen(s),mx=0,id=0,tl=0,str[tl++]=‘$‘,str[tl++]=‘#‘;
13         for(i=0;i<len;i++)str[tl++]=s[i],str[tl++]=‘#‘;
14         for(i=2,str[tl]=0,ans=0;i<tl;i++){
15             p[i]=mx>i?min(p[(id<<1)-i],mx-i):1;
16             while(str[i-p[i]]==str[i+p[i]])p[i]++;
17             if(i+p[i]>mx)mx=i+p[i],id=i;
18         }
19     }
20 }M;
21 char s[N];
22 int dp[N*2][4],ans;
23 
24 void add(int op,int l,int r,int v)
25 {
26     if(l>r)return;
27     dp[l][op]=(dp[l][op]+v)%P;
28     dp[r+1][op]=(dp[r+1][op]-v)%P;
29 }
30 
31 int main(){
32     while(~scanf("%s",s))
33     {
34         memset(dp,0,sizeof(dp));
35         M.maxlen(s);
36         F(i,1,M.tl-2)
37         {
38             add(0,i,M.p[i]+i-1,i);
39             add(1,i,M.p[i]+i-1,1);
40             add(2,i-M.p[i]+1,i,i);
41             add(3,i-M.p[i]+1,i,1);
42         }
43         F(j,1,M.tl)F(i,0,3)dp[j][i]=(dp[j][i]+dp[j-1][i]+P)%P;
44         ans=0;
45         for(int i=4;i<M.tl;i+=2)
46         {
47             ll a=(dp[i][2]-1ll*dp[i][3]*(i/2)%P+P)%P;
48             ll b=(dp[i-2][0]-1ll*dp[i-2][1]*((i-2)/2)%P+P)%P;
49             ans=(a*b%P+ans)%P;
50         }
51         printf("%d\n",ans);
52     }
53     return 0;
54 }