hdu_4734_F(x)(数位DP水)

题目连接：http://acm.hdu.edu.cn/showproblem.php?pid=4734

题意：给你一个F(x)的定义，然后给你a,b，问你在0到b包括b有多少个数满足F(x)<=F(a)

题解:dp[i][j]为dp到第i位的和为j的方案

 #include<cstdio>
 #include<cstring>
 #define F(i,a,b) for(int i=a;i<=b;i++)

 int t,a,b,fa,dp[][],ct,dig[],len;

 int dfs(int pos,int sum,bool inf){
     if(!pos)return ;
     if(!inf&&dp[pos][sum]!=-)return dp[pos][sum];
     int end=inf?dig[pos]:,ans=,tp;
     F(i,,end){
         tp=sum-i*(<<(pos-));
         if(tp>)ans+=dfs(pos-,tp,inf&&(i==end));
     }
     if(!inf)dp[pos][sum]=ans;
     return ans;
 }

 int main(){
     scanf("%d",&t);
     memset(dp,-,sizeof(dp));
     F(ic,,t){
         printf("Case #%d: ",ic);
         scanf("%d%d",&a,&b);
         for(fa=ct=;a;a/=,ct++)fa+=a%*(<<ct);
         for(len=;b;b/=)dig[++len]=b%;
         printf("%d\n",dfs(len,fa+,));
     }
     return ;
 }