学步园

#include <iostream>
#include <cstring>
#include <cstdio>
#include <cstdlib>
using namespace std;
const int MAX = 1000010;
char s[MAX];
char ss[MAX<<1];
int dp[MAX<<1];

int solve(int len)
{
    int ans = 0;
    int right = -1;
    int id = -1;
    for(int i=0; i<len; i++)
    {
        int r = 1;
        if(right >= i)
            r = max(r, min(right-i+1, dp[2*id-i]));
        while((i-r+1>=0&&i+r-1<len)&&(ss[i-r+1]==ss[i+r-1]))
            r++;
        r--;
        if(i+r-1 > right)
        {
            right = i+r-1;
            id = i;
        }
        dp[i] = r;
        if(ans < r)
            ans = r;
    }
    return ans - 1;
}


int main()
{
	// freopen("in","r",stdin);
	// freopen("out","w",stdout);
    while(scanf("%s", s) != EOF)
    {
        int len = strlen(s);
        int cnt = 0;
        for(int i=0; i<len; i++)
        {
            ss[cnt++] = '#';
            ss[cnt++] = s[i];
        }
        ss[cnt++] = '#';

        printf("%d\n", solve(cnt));
    }
    return 0;
}