Codeforce 7D Palindrome Degree

本文介绍了一个使用Manacher算法解决回文子串问题的C++实现案例。通过预处理字符串并运用Manacher算法,该程序有效地计算了所有奇数长度回文子串的数量,并通过递推计算出所有偶数长度回文子串的数量。

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Manacher+递推  裸题。。。

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <queue>
#include <vector>
using namespace std;

#define N 5000010

int n,p[N*2],Dp[N];
char S[N*2];
long long Ans;

void Manacher()
{
    int m=0,x=1;
    for(int i=1;i<=n;i++)
    {
        p[i]=1;
        if(m>i)
            p[i]=min(m-i,p[2*x-i]);
        while(S[i-p[i]]==S[i+p[i]])
            p[i]++;
        if(i-p[i]+1==1&&p[i]!=1)
        {
            Dp[p[i]-1]=Dp[(p[i]-1)/2]+1;
            Ans+=Dp[p[i]-1];
        }
        if(m<i+p[i]-1)
            m=i+p[i]-1,x=i;
    }
}

int main()
{
    scanf("%s",S);
    n=(int)strlen(S);
    for(int i=n;i>=0;i--)
        S[i*2+2]=S[i],S[i*2+1]='#';
    S[0]='$';
    n=n*2+1;
    Manacher();
    cout<<Ans<<endl;
    return 0;
}



### Codeforces Problem or Contest 998 Information For the specific details on Codeforces problem or contest numbered 998, direct references were not provided within the available citations. However, based on similar structures observed in other contests such as those described where configurations often include constraints like `n` representing numbers of elements with defined ranges[^1], it can be inferred that contest or problem 998 would follow a comparable format. Typically, each Codeforces contest includes several problems labeled from A to F or beyond depending on the round size. Each problem comes with its own set of rules, input/output formats, and constraint descriptions. For instance, some problems specify conditions involving integer inputs for calculations or logical deductions, while others might involve more complex algorithms or data processing tasks[^3]. To find detailed information regarding contest or problem 998 specifically: - Visit the official Codeforces website. - Navigate through past contests until reaching contest 998. - Review individual problem statements under this contest for precise requirements and examples. Additionally, competitive programming platforms usually provide comprehensive documentation alongside community discussions which serve valuable resources when exploring particular challenges or learning algorithmic solutions[^2]. ```cpp // Example C++ code snippet demonstrating how contestants interact with input/output during competitions #include <iostream> using namespace std; int main() { int n; cin >> n; // Process according to problem statement specifics } ```
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