【51NOD-0】1089 最长回文子串 V2(Manacher算法)
【算法】回文树
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#include<cstdio> #include<algorithm> #include<cstring> using namespace std; const int maxn=100010; struct trees{int len,fail,t[260];}t[maxn]; char s[maxn]; int n,len,l,sz,ans; int getfail(int x) { while(s[len-t[x].len-1]!=s[len])x=t[x].fail; return x; } void tree_work() { int x=s[++len]; l=getfail(l); if(!t[l].t[x]) { sz++; t[sz].len=t[l].len+2; if(t[sz].len>ans)ans=t[sz].len; t[sz].fail=t[getfail(t[l].fail)].t[x];//偏小 t[l].t[x]=sz; } l=t[l].t[x]; } int main() { scanf("%s",s+1); n=strlen(s+1); sz=1; s[0]=-1;// t[0].len=0;t[1].len=-1; t[0].fail=t[1].fail=1; len=l=ans=0; for(int i=1;i<=n;i++)tree_work(); printf("%d",ans); return 0; }