51nod1089 最长回文子串 V2(Manacher算法)

链接:http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1089

题意:中文题。

分析:Manacher算法练习题。

代码:

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
const int N=200010;
const int mod=100000000;
const int MOD1=1000000007;
const int MOD2=1000000009;
const double EPS=0.00000001;
typedef long long ll;
const ll MOD=998244353;
const int INF=1000000010;
const ll MAX=1000000000000;
const double pi=acos(-1.0);
typedef double db;
typedef unsigned long long ull;
char s[N];
int p_ma[N];
void Manacher(char s[],int les) {
    int i,mx,id;
    for (i=les-1;i>=0;i--) {
        s[2*i+2]=s[i];s[2*i+3]='#';
    }
    mx=id=0;s[1]=s[2*les+2]='#';les*=2;
    for (i=1;i<=les;i++) {
        if (mx>i) p_ma[i]=min(p_ma[id*2-i],mx-i);
        else p_ma[i]=1;
        for (;i-p_ma[i]>0&&s[i-p_ma[i]]==s[i+p_ma[i]];p_ma[i]++ );
        if (i+p_ma[i]>mx) {
            mx=i+p_ma[i];id=i;
        }
    }
}
int main()
{
    int i,len,ans=0;
    scanf("%s", s);
    len=strlen(s);
    Manacher(s,len);
    for (i=1;i<=2*len+2;i++) ans=max(ans,p_ma[i]-1);
    printf("%d\n", ans);
    return 0;
}


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