[HDU-4734] F(x)

题目链接

这个题十分简单，关键是F(x)定义的那种感觉

#include <iostream>
#include <cstring>
#include <cstdio>
#include <bits/stdc++.h>
using namespace std;
int b[21];
int l,r;
int dp[21][50001];
int F(int x)
{
	int tot=1;
	int ans=0;
	while(x)
	{
		ans+=tot*(x%10);
		x/=10;
		tot<<=1;
	}
	return ans;
}
int dfs(int pos,int preok,int sup)
{
	if(pos==-1) return 1;
	if(preok&&dp[pos][sup]!=-1) return dp[pos][sup];
	int up=preok?9:b[pos],sum=0;
	for(int i=0;i<=up;i++)
	{
		if(sup-i*(1<<pos)>=0) 
		sum+=dfs(pos-1,preok||i<b[pos],sup-i*(1<<pos));
	}
	if(preok) return dp[pos][sup]=sum;
	return sum;
}
int solve(int R)
{
	int tot=0;
	while(R)
	{
		b[tot++]=R%10;
		R/=10;
	}
	int sum=dfs(tot-1,0,F(l));
	return sum;
}
int main()
{
	int n;
	memset(dp,-1,sizeof(dp));
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>l>>r;
		printf("Case #%d: %d\n",i,solve(r));
	}
}