PAT T1025 Keep at Most 100 Characters

删除字符的镜像问题，状态转移方程一样~

#include<bits/stdc++.h>
using namespace std;
const int maxn=;
const int mod=1e9+;
string s;
long long dp[maxn][maxn];
int main () {
    cin>>s;
    fill (dp[],dp[]+maxn,);
    int t=max(,(int)(s.length()-));
    for (int i=;i<s.length();i++) {
        for (int j=i;j<=s.length();j++) {
            dp[i][j]=dp[i][j-]%mod+dp[i-][j-]%mod;
            dp[i][j]%=mod;
            for (int k=j-;j-k<=i;k--) {
                if (s[k-]==s[j-]) {
                    dp[i][j]-=dp[i-(j-k)][k-];
                    break;
                }
            }
        }
    }
    long long sum=;
    for (int i=t;i<s.length();i++) {
        sum+=dp[i][s.length()];
        sum%=mod;
    }
    printf ("%lld",sum);
    return ;
}