hdu4632 Palindrome subsequence 区间DP

hdu4632 多校4场题目区间dp
定义变量 f[i][j],表示在区间 i到j的回文串的个数(注:i,j为字符串下标)
则对于区间i- j 如果s[i]==s[j] f[i][j]=f[i+1][j]+f[i][j-1]-f[i+1][j-1]+f[i +1][j-1]+1=f[i+1][j]+f[i][j+1]+1;
如果 s[i]!=s[j] 那么 f[i][j]=f[i+1][j]+f[i][j-1]-f[i+1][j-1];
代码如下：

 1 #include<iostream>
 2 #include<cstdlib>
 3 #include<cstdio>
 4 #include<cstring>
 5 #include<string>
 6 using namespace std;
 7 #define MAX 1010
 8 #define M 10007
 9 int f[MAX][MAX];
10 void init()
11 {
12     memset(f,0,sizeof(f));
13     for(int i=0;i<MAX;i++)
14         f[i][i]=1;
15 }
16 int main()
17 {
18     string s;
19     int t;
20     cin>>t;
21     int k=1;
22     while(t--)
23     {
24         cin>>s;
25         int n=s.length()-1;
26         init();
27         for(int j=0;j<=n;j++)
28             for(int i=j-1;i>=0;i--)
29             {
30                 if(s[i]==s[j]) f[i][j]=(f[i+1][j]+f[i][j-1]+1)%M;
31                 else 
32                 if(s[i]!=s[j]) f[i][j]=(f[i][j-1]+f[i+1][j]-f[i+1][j-1]+M)%M;
33             }
34         cout<<"Case "<<k++<<": "<<f[0][n]<<endl;
35     }
36     return 0;
37 }

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