hdu4513 （manacher）

题意：求最长回文子串，且从最左到mid是单调不降的。基本同manacher板子，就加了一个条件：

s[i+p[i]]<=s[i+p[i]-2]

#include <cstdio>#include <cstring>#define N 100010inline int read(){int x=0,f=1;char ch=getchar();while(ch<'0'||ch>'9'){if(ch=='-') f=-1;ch=getchar();}while(ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();return x*f;}template <typename T>inline T min(T x,T y){return x<y?x:y;}int n,p[N<<1],s[N<<1];int main(){//freopen("a.in","r",stdin);int tst=read();while(tst--){int len=read();n=0;for(int i=1;i<=len;++i) s[++n]=300,s[++n]=read();s[++n]=300;int id=0,mx=0,ans=0;for(int i=1;i<=n;++i){if(i<mx) p[i]=min(p[(id<<1)-i],mx-i);else p[i]=1;while(i-p[i]>=1&&i+p[i]<=n&&s[i-p[i]]==s[i+p[i]]&&s[i+p[i]]<=s[i+p[i]-2]) ++p[i];if(i+p[i]>mx) mx=i+p[i],id=i;if(p[i]>ans) ans=p[i];}printf("%d\n",ans-1);}return 0;}