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[11][200001],ct,dig[11],len;

int dfs(int pos,int sum,bool inf){
    if(!pos)return 1;
    if(!inf&&dp[pos][sum]!=-1)return dp[pos][sum];
    int end=inf?dig[pos]:9,ans=0,tp;
    F(i,0,end){
        tp=sum-i*(1<<(pos-1));
        if(tp>0)ans+=dfs(pos-1,tp,inf&&(i==end));
    }
    if(!inf)dp[pos][sum]=ans;
    return ans;
}

int main(){
    scanf("%d",&t);
    memset(dp,-1,sizeof(dp));
    F(ic,1,t){
        printf("Case #%d: ",ic);
        scanf("%d%d",&a,&b);
        for(fa=ct=0;a;a/=10,ct++)fa+=a%10*(1<<ct);
        for(len=0;b;b/=10)dig[++len]=b%10;
        printf("%d\n",dfs(len,fa+1,1));
    }
    return 0;
}