hdu 3068 最长回文 (Manacher算法)

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mannacher算发的处理要将字符串的各个字母之间加上'#' a[0]='$' a[2*len+1]='#' a[2*len+2]='#'

#include<iostream>#include<math.h>#include<stdio.h>#include<algorithm>#include<string.h>#include<vector>#include<map>using namespace std;//typedef long long lld;const int oo=0x3f3f3f3f;//const lld OO=1LL<<61;const int MOD=(1e9)+7;const int maxn=110005;char str[maxn],a[maxn<<2];int p[maxn<<1];void init_string(int len){    a[0]='$';    for(int i=1;i<=len;i++)    {        a[2*i-1]='#';        a[2*i]=str[i];    }    a[2*len+1]='#';    a[2*len+2]='#';}int Manacher(int len){    int mx = 0, id = 0;    for (int i = 1; i <= len; i++)    {        if (mx > i)            p[i] = min(mx - i, p[2 * id - i]);        else            p[i] = 1;        while (a[i - p[i]] == a[i + p[i]])            p[i]++;        if (p[i] + i > mx)        {            mx = p[i] + i;            id = i;        }    }    int ans=0;    for(int i=1;i<=len;i++)    {        ans=max(ans,p[i]-1);    }    return ans;}int main(){    while(scanf("%s",str+1)!=EOF)    {        int n=strlen(str+1);        init_string(n);        cout<<Manacher(2*n+1)<<endl;    }    return 0;}/**abcd-> abcdabcabcda*/

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