HDU3068 最长回文

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 const int N=250010;
 4 char s[N],ss[N];
 5 int RL[N];
 6 int calc(){
 7     ss[0]=‘#‘;
 8     for(int i=1,i_end=strlen(s);i<=i_end;++i){
 9         ss[(i<<1)-1]=s[i-1];
10         ss[(i<<1|1)-1]=‘#‘;
11     }
12     int len=strlen(s)<<1|1;
13     int MaxRight=0,pos=0,maxlen=0;
14     for(int i=0;i<=len;++i){
15         if(i<MaxRight)RL[i]=min(RL[(pos<<1)-i],MaxRight-i);
16         else RL[i]=1;
17         
18         while(i-RL[i]>=0&&i+RL[i]<=len&&ss[i-RL[i]]==ss[i+RL[i]])++RL[i];
19         if(RL[i]+i-1>MaxRight)
20             MaxRight=RL[i]+i-1,pos=i;
21         maxlen=max(maxlen,RL[i]);
22     }
23     return maxlen-1;
24 }
25 int main(){
26     while(~scanf("%s",s))
27         printf("%d\n",calc());
28     return 0;
29 }