Codeforces Round #311 (Div. 2) E. Ann and Half-Palindrome (DP + dictionary tree)

Codeforces Round #311 (Div. 2) E. Ann and Half-Palindrome (DP + dictionary tree)

Question address: Portal
Use dp to obtain all the required semi-return strings and mark them. Then construct the dictionary tree. Then, the dfs finds the Subtrees and Subtrees of all nodes, and then finds the k th node.
The Code is as follows:

#include 
  
   #include 
   
    #include 
    
     #include 
     
      #include #include 
      
       #include
       #include 
        
         #include 
         
          #include 
          
           using namespace std;#define LL __int64#define pi acos(-1.0)//#pragma comment(linker, /STACK:1024000000)const int mod=1e9+7;const int INF=0x3f3f3f3f;const double eqs=1e-9;const int MAXN=400000+10;int ok[5001][5001];int k, cnt;char s[6000], str[6000];struct node{ int flag, sum; node *next[2];};node *newnode(){ int i; node *p=new node; for(i=0;i<2;i++){ p->next[i]=NULL; } p->flag=0; p->sum=0; return p;}void Insert(int st, int len, node *root){ int i, x; node *p=root; for(i=st;i
           
            next[x]==NULL) p->next[x]=newnode(); p=p->next[x]; if(ok[st][i]) { p->flag++; p->sum++; } }}void dfs(node *u){ for(int i=0;i<2;i++){ if(u->next[i]!=NULL){ dfs(u->next[i]); u->sum+=u->next[i]->sum; } }}void seach(node *root){ node *p=root; while(1){ k-=p->flag; if(k<=0){ return ; } if(p->next[0]!=NULL){ if(p->next[0]->sum>=k){ str[cnt]='a'; p=p->next[0]; cnt++; continue ; } else k-=p->next[0]->sum; } str[cnt]='b'; p=p->next[1]; cnt++; }}int main(){ int i, j, len, h; while(scanf(%s,s)!=EOF){ scanf(%d,&k); len=strlen(s); memset(ok,0,sizeof(ok)); for(i=0;i