POI 2010 Antisymmetry

Posted 2020-11-21 evenbao

【题目链接】

           https://www.lydsy.com/JudgeOnline/problem.php?id=2084

【算法】

           manacher

【代码】

           

#include<bits/stdc++.h>
using namespace std;
#define MAXN 500010

int n;
char s[MAXN];

inline void Manacher()
{
        int i,len,mx = 0,pos = 0;
        long long ans = 0;
        static char tmp[MAXN<<1];
        static int p[MAXN<<1];
        len = strlen(s+1);
        for (i = 1; i <= len; i++)
        {
                tmp[2*i-1] = ‘#‘;
                tmp[2*i] = s[i];
        }
        tmp[len = 2 * len + 1] = ‘#‘;
        for (i = 1; i <= len; i++)
        {
                if (tmp[i] != ‘#‘)
                {
                        p[i] = 1;
                        continue;
                }
                if (mx > i) p[i] = min(p[2*pos-i],mx-i);
                else p[i] = 1;
                while (i - p[i] >= 1 && i + p[i] <= len && ((tmp[i-p[i]] == ‘#‘ && tmp[i+p[i]] == ‘#‘) || (tmp[i-p[i]] != tmp[i+p[i]]))) p[i]++;
                if (i + p[i] - 1 > mx)
                {
                        mx = i + p[i] - 1;
                        pos = i;
                }
        }        
        for (i = 1; i <= len; i++) 
        {
                if (tmp[i] == ‘#‘)
                        ans += (long long)(p[i] - 1) / 2;
        }
        printf("%lld
",ans);
}

int main() 
{
        
        scanf("%d%s",&n,s+1);
        Manacher();
        
        return 0;
    
}