HDU 3068 最长回文（manacher算法）

分析：

求最长回文子串     区别于最长回文子序列      manacher算法（网上都有详细解释）   直接上代码

AC代码：

#include <iostream>#include <stdlib.h>#include <stdio.h>#include <string.h>#include <math.h>#include <vector>#include <stack>#include <queue>#include <map>#include <set>#include<list>#include <bitset>#include <climits>#include <algorithm>#define gcd(a,b) __gcd(a,b)#define FINfreopen("input.txt","r",stdin)#define FOUT freopen("output.txt","w",stdout)typedef long long LL;const LL mod=1e9+7;const int INF=0x3f3f3f3f;const double PI=acos(-1.0);using namespace std;char str[2200010];int p[2200010];int main (){//FIN;while (scanf("%s",&str)!=EOF){if (str[0]==' ')continue;int n=strlen(str);for (int i=n-1;i>=0;i--){//     处理串 str[(i+1)*2+1]='#';str[(i+1)*2]=str[i];}str[1]='#';str[0]='!';int id=0;int ans=0;memset(p,0,sizeof(p));for (int i=2;i<=n*2+1;i++){//                  核心代码 p[i]=p[id]+id>i?min(p[2*id-i],p[id]+id-i):1;while (str[i-p[i]]==str[i+p[i]]) p[i]++;if (i+p[i]>id+p[id]) id=i;if (ans<p[i]) ans=p[i];}printf ("%d\n",ans-1);}return 0;}