1040 Longest Symmetric String dp

Given a string, you are supposed to output the length of the longest symmetric sub-string. For example, given Is PAT&TAP symmetric?, the longest symmetric sub-string is s PAT&TAP s, hence you must output 11.

Input Specification:

Each input file contains one test case which gives a non-empty string of length no more than 1000.

Output Specification:

For each test case, simply print the maximum length in a line.

Sample Input:

Is PAT&TAP symmetric?

Sample Output:

11
我的错误代码

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#define inf 105
using namespace std;
int main()
{
    string s;
    int n,dp[inf][inf],maxn=0;
    getline(cin,s);
    n=s.size();
    fill(dp[0],dp[0]+inf*inf,0);
    for(int i=0;i<n;i++)
    for(int j=0;j<n;j++)
    {
        if(i==j)
        dp[i][j]=1;
        //if(j-i==1&&s[j]==s[i])
        //dp[i][j]=1;
    }
    for(int i=0;i<n;i++)
        for(int j=i+1;j<n;j++)
        {
            if(s[i]==s[j])
            {
                dp[i][j]=dp[i+1][j-1]+1;
                if(dp[i][j]>maxn)
                maxn=dp[i][j];
            }
            
            else
            dp[i][j]=0;
        }
        cout<<maxn<<endl;    
        return 0;
}

柳神代码

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#define inf 1001
using namespace std;
int main()
{
    string s;
    int n,dp[inf][inf],ans=1;
    getline(cin,s);
    n=s.size();
    fill(dp[0],dp[0]+inf*inf,0);
    for(int i=0;i<n;i++)
    {
        dp[i][i]=1;
        if(s[i]==s[i+1]&&i<n-1)
        {
        dp[i][i+1]=1;
        ans=2;
    }
    }
    for(int l=2;l<=n;l++)
        for(int i=0;l+i-1<n;i++)
        {
            int j=l+i-1;
            if(s[i]==s[j]&&dp[i+1][j-1]==1)
            {
                dp[i][j]=1;
                ans=l;
            }
        }
        cout<<ans<<endl;    
        return 0;
}

dp还得好好学习啊

思维不行