字符串算法 Manacher

 1.字符串字符之间补#

 2.遍历就好了

 

//O(n) manacher算法 
 #include<iostream>
using namespace std;
#define INF 0x7f
const int N =10005; 
typedef long long ll ;
#define f(i,l,r) for(int i=l;i<=r;++i)
#define g(i,l,r) for(int i=l;i>=r;--i)
 
 
int l,len,p[N<<1];
char s[N],S[N<<1];
void manacher(){
	 scanf("%s",s);len=strlen(s);
    l=-1;
    for(int i=0;i<len;i++) S[++l]='#',S[++l]=s[i];
    S[++l]='#';

	int ans =0 ,id =0,mx=-1;
	f(i,1,l-1){
		if(id+mx>i)
			p[i]=min(p[id*2-i],id+mx-i);
		while(i-p[i]-1>=0&&i+p[i]+1<=l&&S[i-p[i]-1]==S[i+p[i]+1])
			p[i]++;
		if(id+mx <i+p[i])
			id=i,mx=p[i];
		ans=max(ans,p[i]); 
    }
   
    printf("%d\n",ans);
}