CF245H Queries for Number of Palindromes

对字符串s，多次询问，给你两个数L和R，问在字符串区间l到r的字串中，包含多少回文串。

 

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#include <iostream> #include<queue> #include <cstring> #define IOS std::ios::sync_with_stdio(0) using namespace std;  const int N =5003;     int vis[N][N],pal[N][N];  int f[N][N];  string s;  int n;  int test(int a,int b){      if(a>=b) return 1;      if(s[a]!=s[b]) return 0;      if(vis[a][b]) return pal[a][b];      vis[a][b]=1;             return pal[a][b]=test(a+1,b-1);  }  void solve(){     int i,j,tes;     cin>>s>>tes; n=s.size();     s=" "+s;           for(int i=1;i<=n;i++)    f[i][i]=1;                          for(int i=1;i<=n-1;i++)  f[i][i+1]=(s[i]==s[i+1]?3:2);           for(i=n-2;i>=1;i--)      for(j=i+2;j<=n;j++)       f[i][j]=(f[i+1][j]+f[i][j-1]-f[i+1][j-1]+(test(i,j)?1:0));           while(tes--){         int x,y;         cin>>x>>y;         cout<<f[x][y]<<endl;     }  }  signed main(){      IOS;      solve();  }